Terms of use

These terms consist of two parts. Part A applies identically to all Windows programs by Timo Britz. Part B contains the details for Mietfix: price, trial mode, network connections, scope of the licence and description of performance. In the event of contradictions, Part B takes precedence.

How to withdraw from a purchase is set out in section A 4.

Part A · General licence and terms of use

A 1 Provider and scope

(1) The provider and rights holder of the programs is:

Timo Britz
Sülzgürtel 47
50937 Köln
Germany
Phone +49 162 1655800
E-mail info@timobritz.de

The other mandatory information can be found in the legal notice.

(2) These terms apply to the provision and use of the Windows programs by Timo Britz, both in trial mode and with a licence certificate. For each program, its product part (Part B) applies in addition. In the event of contradictions, the product part takes precedence.

(3) Definitions:

• Program: the respective Windows program in all releases of a major version, for example 1.0, 1.1 and 1.7.2 for major version 1.
• Licence certificate: an electronically signed text file that is issued in your name and unlocks the program for a major version without expiry.
• Store licence: the entitlement to use a program bought in the Microsoft Store. It is tied to the Microsoft account used for the purchase.
• Trial mode: use without a licence certificate to the extent set out in the product part.
• Consumer (Verbraucher): any natural person who enters into a legal transaction for purposes that predominantly are outside their trade, business or profession (section 13 BGB).

A 2 Contractual partner and conclusion of the contract

(1) The program can be downloaded free of charge from the product page. What is purchased is not the download but a licence certificate.

(2) Purchase via Digistore24. The purchase button on the product page takes you to the Digistore24 order form. If Digistore24 acts there as a reseller, the Digistore24 group company named in the order form (depending on the country, Digistore24 GmbH, Hildesheim, or one of its sister companies) is your contractual partner. It sells the licence certificate in its own name and for its own account, processes the payment and issues the invoice. The purchase contract is then additionally governed by its general terms and conditions and its privacy policy, which are shown in the order form. If the order form names me as the seller, I am your contractual partner.

(2a) Purchase in the Microsoft Store. If a program is offered in the Microsoft Store, you can buy it there. Your contractual partner for this purchase is then the Microsoft company named in the Store (in the European Economic Area, according to the Microsoft Store terms of sale, Microsoft Ireland Operations Limited, Dublin). It handles payment and issues the invoice; its terms of sale and its privacy statement also apply to the purchase contract. The Store licence takes the place of the licence certificate; what these terms say about the licence certificate applies to it accordingly, unless otherwise provided.

(3) Purchase directly from me. Where the product part provides for this, you can also buy the licence certificate directly from me. The presentation on the product page does not constitute a binding offer. A message sent via the contact form or by e-mail is a non-binding enquiry. In response, you will receive an offer by e-mail together with an invoice and these terms. The contract is concluded when you accept the offer by e-mail. I am then your contractual partner.

(4) In these terms, “your contractual partner” is the party with which you concluded the purchase contract under paragraph 2, 2a or 3. In every case, the right to use the program is granted by me (A 6); these terms govern it even if the purchase contract is concluded with Digistore24 or in the Microsoft Store.

(5) The language of the contract is German. For a purchase directly from me, I do not store the contract text in a form accessible to you; you receive it with the offer by e-mail and can save or print it.

A 3 Price, payment and delivery

(1) The price is stated in the product part and on the product page. It is a one-off payment for a licence certificate for major version 1. There is no term, no renewal and no recurring payment. No further costs arise; nothing is shipped.

(2) VAT. I am a small business owner (Kleinunternehmer) within the meaning of section 19 UStG (German VAT Act) and do not charge VAT. For a purchase directly from me, the stated price is therefore the final price without VAT. For a purchase via Digistore24 as reseller, Digistore24 calculates the VAT; the total price shown in the order form is authoritative.

(3) Payment. For a purchase via Digistore24, the order form shows the available payment methods. For a purchase directly from me, you pay by bank transfer after receiving the invoice.

(4) Delivery. You receive the licence certificate as a text file by e-mail to the address given with the order, at the latest within two working days of receipt of payment. If I issue it by hand, this usually happens on the same working day. Whether a program issues the certificate automatically is set out in the product part (B 2). For a purchase via Digistore24, receipt of payment means the payment confirmation from Digistore24; for payment by bank transfer or prepayment, this is its receipt by Digistore24.

(5) The licence certificate is issued in the name given with the order and, if a company or school is stated, additionally in its name. It contains the name, the licence number, the date of issue and, where applicable, your e-mail address in plain text. Until the certificate arrives, the program continues to run in trial mode.

(6) Purchase in the Microsoft Store. The final price shown there, including VAT, applies; the Store shows the payment methods. Paragraphs 2 to 5 do not apply to it. The program is delivered via the Store and unlocked with the Store licence.

A 4 Withdrawal (Widerruf)

A 4.1 Purchase via Digistore24

For a purchase via Digistore24, Digistore24 is your contractual partner (A 2(2)). Whether and how you can withdraw from the purchase is governed solely by the withdrawal policy (Widerrufsbelehrung) of Digistore24. It is shown in the order form and sent with the order confirmation, and the Digistore24 terms for buyers and its withdrawal page make it available. You declare the withdrawal to Digistore24, for example via the “Vertrag widerrufen” (withdraw from contract) button provided there. Digistore24 then also refunds the price. There is no separate withdrawal policy of mine for these purchases.

A 4.2 No waiver of the right of withdrawal (Widerrufsrecht)

For a purchase via Digistore24 and for a purchase directly from me, no waiver of the right of withdrawal is requested, i.e. no consent by which it would expire early upon delivery of the licence certificate. Consumers can therefore withdraw from the contract within the statutory period of 14 days even after receiving the licence certificate.

A 4.3 Purchase directly from me

If you buy a licence certificate directly from me (A 2(3); currently only Aktenlage on request), the following applies: my withdrawal policy with model withdrawal form. It is also enclosed with the offer.

A 4.4 After withdrawal

Upon the refund, your right to use the program with the refunded licence certificate or the refunded Store licence ends. Please then remove any licence certificate from the program and delete your copies of it. The program then continues to run in trial mode; access to your data is retained (A 7). Independently of this, you can test every program before buying it, free of charge and without a time limit, in trial mode (A 5).

A 4.5 Purchase in the Microsoft Store

For a purchase in the Microsoft Store, the Microsoft company named there is your contractual partner (A 2(2a)). Whether and how you can withdraw from the purchase or request a refund is governed by its withdrawal policy and its terms of sale. You declare the withdrawal to it. There is no separate withdrawal policy from me for these purchases.

A 5 Trial mode

(1) Without a licence certificate, the program runs in trial mode. Trial mode is free of charge and not time-limited. What it limits is set out in the product part (B 2); all other functions are available.

(2) These terms apply to trial mode with one deviation: since it is free of charge, I am liable for defects only if I have fraudulently concealed them (arglistig verschwiegen), and otherwise only for intent (Vorsatz) and gross negligence (grobe Fahrlässigkeit). Liability for damage resulting from injury to life, body or health and liability under the German Product Liability Act (Produkthaftungsgesetz) remain unaffected.

A 6 Right of use (licence)

(1) With the licence certificate or the Store licence you receive a simple, non-exclusive and perpetual right, covering use of the program in all releases of the acquired major version. A new major version is not included; your release then continues to run unchanged.

(2) The licence applies to one person and their own computers, for use for their own purposes. Deviations are set out in the product part (B 6).

(3) Passing on. You may not pass the licence certificate on to third parties as long as you use the program yourself. If you give up use permanently, you may transfer the licence in full to another person; you then delete your own copies of the licence certificate. The same applies in the event of inheritance. On request, I issue the new holder a certificate in their name.

(4) Replacement certificate. If your licence certificate is lost, I reissue it free of charge with the same number for as long as I keep the register of certificates issued (see privacy policy).

(5) No activation. For the licence certificate, there is no activation, no account and no server that unlocks anything. The program checks the licence certificate on your computer without a network connection and displays the name from the licence certificate. There is no further copy protection. The program checks a Store licence via Windows and the Microsoft Store; a Microsoft account may be required for this. Paragraphs 3 and 4 apply only to the licence certificate; whether a Store licence can be transferred is governed by the terms of the Microsoft Store.

(6) The rights under sections 69d and 69e UrhG (German Copyright Act) remain unaffected, in particular reverse engineering to the extent permitted by law.

(7) Third-party components are subject to their own licences (A 13).

A 7 Access to your data

A 8 Updates

(1) For all releases of major version 1, I provide updates including security updates for the period you can reasonably expect under section 327f BGB. New features and adaptations to future versions of Windows are only included where they are necessary for security or for operation in accordance with the contract. For purchases up to 6 October 2026, the commitment in the version in force at the time (security updates until at least 31 December 2028) continues to apply.

(2) The statutory obligation to provide updates for the period you can expect given the type and purpose of the program (section 327f BGB) remains unaffected.

(3) I provide information about available updates on the product page. Whether and how the program itself points out new releases is set out in the product part (B 8).

(4) Updates within the major version are free of charge. You decide whether to install an update. For an update that you do not install within a reasonable period, section 327f(2) BGB applies.

(5) You can report security vulnerabilities to me at info@timobritz.de.

A 9 Defects

(1) In the event of defects, you have the statutory rights, with regard to consumers in particular under the provisions on contracts for digital products (sections 327 et seq. BGB). They are directed against your contractual partner: for a purchase via Digistore24, against Digistore24; for a purchase in the Microsoft Store, against the Microsoft company named there; for a purchase directly from me, against me. These terms do not restrict these rights.

(2) Irrespective of this, you can report errors to me at any time at info@timobritz.de. Where possible, I remedy defects in the program by means of updates within the scope of A 8.

A 10 What the programs do and what they do not do

(1) The following paragraphs and the section “Description of performance” in the product part (B 10) describe what the programs do. They are not exclusions of liability and do not restrict the rights under A 9.

(2) Suggestions, not decisions. Where a program recognises, classifies, calculates or formulates, it presents suggestions. The decision is made by the person operating the program. The programs do not provide legal, tax, investment or medical advice.

(3) Language model. Programs with an optional language model mark in the program what the language model has contributed (product part). Such contributions may be incorrect. The language model runs on your computer. Whether it is shipped with the program or downloaded when you press a button is set out in the product part. How quickly it responds depends on your computer’s hardware.

(4) Data backup. The programs do not replace a data backup. Built-in backups are stored on the same computer unless the product part states otherwise. They help against input errors, not against hardware failure, theft or malware.

(5) Operating system. The programs run only on Microsoft Windows. The system requirements are set out in the product part (B 5).

(6) Installer without code signature. The installers do not carry a code signature. Windows may show a warning on first launch; if Windows Smart App Control is switched on, Windows may prevent execution. This does not apply to programs from the Microsoft Store; their packages are signed by Microsoft.

A 11 Liability

(1) I am liable without limitation

• in cases of intent and gross negligence,
• for damage resulting from injury to life, body or health,
• where a guarantee has been assumed,
• under the German Product Liability Act and
• insofar as mandatory statutory provisions impose liability.

(2) In the event of a slightly negligent breach of an essential contractual obligation (wesentliche Vertragspflicht), the fulfilment of which makes the proper performance of the contract possible in the first place and on whose observance you may rely, liability is limited to the typical damage foreseeable at the time the contract was concluded. Otherwise, liability for slight negligence is excluded.

(3) Loss of data. For the loss of data, I am liable only up to the amount that would have been required to restore it had you backed up your data regularly and in a manner appropriate to the risk. This does not apply in the cases of paragraph 1.

(4) For trial mode, A 5(2) applies. Mandatory rights of consumers remain unaffected.

A 12 Data protection

The programs do not transmit any content to me. The connections a program makes are set out in the product part (B 4). The data I process when you make a purchase, when I issue the licence certificate and for additional services described in the product part is set out in the privacy policy.

A 13 Third-party components

The programs contain free software and free content from third parties. The product part names the most important ones (B 9). The full licence texts are included with the program and, after installation, can be found in the program folder under Lizenzen-Dritter. These licences apply to the respective components independently of these terms and take precedence for them.

A 14 Versions of these terms

A contract that has been concluded is governed by the version of these terms valid when it was concluded; trial mode is governed by the version valid at installation. Later versions apply only to contracts concluded thereafter.

A 15 Applicable law and dispute resolution

(1) German law applies, excluding the UN Convention on Contracts for the International Sale of Goods (CISG). With regard to consumers, the mandatory provisions of the country in which they have their habitual residence remain unaffected.

(2) I am neither willing nor obliged to participate in dispute resolution proceedings before a consumer arbitration board.

Part B · Product part Mietfix

B 1 Subject matter

Mietfix is a program for Microsoft Windows with which private landlords prepare the service charge statement (German Betriebskostenabrechnung) for residential buildings with one to about five residential units. Each item states the invoice, the reference in the supporting document, the legal source and the calculation. A change of tenant during the billing year is split to the exact day; the landlord bears vacancy. In addition, there are tools for assessing profitability: investment, repayment schedule and household budget book. The program runs entirely on your computer.

B 2 Price, purchase and trial mode

• Price: €29 one-off for a licence certificate for major version 1; for VAT, see A 3(2).
• Purchase: via Digistore24 (A 2(2)) or, if you acquire Mietfix via the Microsoft Store, there (A 2(2a)). A licence certificate from timobritz.de also unlocks the Microsoft Store version; anyone who has already bought does not pay twice. A purchase directly from me is not provided for.
• Delivery: after receipt of payment, my web server issues the licence certificate automatically, sends it by e-mail and shows it on the confirmation page. If automatic issuing fails, I issue it by hand, usually on the same working day and at the latest within two working days of receipt of payment (A 3(4)). For a purchase in the Microsoft Store, the Store unlocks the program, without a licence certificate.
• Trial mode: without a licence certificate, one building and one billing period can be created. Viewing, preparing statements, printing and exporting are possible even without a licence certificate. The same trial mode applies in the Microsoft Store version; for this, the Store lists Mietfix as a trial without an expiry date.
• The licence certificate is accepted from Mietfix 1.1.0 onwards and applies to all releases 1.x. Anyone using an older release first installs the current release from the product page.

B 3 Data and responsibility

Mietfix stores in the folder %APPDATA%\Mietfix among other things the landlord’s name and address, the tenants’ names with the start and end of the tenancies, the number of occupants per flat, meter readings, third-party invoices and the finished statements. The data is stored unencrypted as readable JSON and PDF files so that it remains readable even without the program. Anyone who shares the computer with others should protect their user account or encrypt the drive (for example with BitLocker). In the Microsoft Store version, the data is stored in the folder Documents\Mietfix. In both versions it is kept when uninstalling; the program does not delete it.

The controller (Verantwortlicher) within the meaning of the General Data Protection Regulation (GDPR) is the landlord, who captures the data. I do not receive this data; there is no server, no copy and no access. I am therefore neither controller nor processor (Auftragsverarbeiter); a data processing agreement is neither necessary nor possible.

B 4 Network connections

• Version check: at most once every seven days, and otherwise at the push of a button, the program retrieves the public timobritz.de/mietfix/fassungen.json file. All that is transmitted is the request with your IP address and the identifier Mietfix, without a licence number or count. The check is switched on by default. It can be switched off in the program under “Rechtliches” (legal) with the “Automatisch nach Updates suchen” (check for updates automatically) switch or with the environment variable MIETFIX_KEINE_ABFRAGE=1, which takes precedence. When it is switched off, the program no longer establishes any connection on its own. The Microsoft Store version has no such check; new releases come via the Store. The program asks Windows whether Mietfix was bought there; whether Windows contacts Microsoft for this is up to Windows.
• Language model: in the AI edition, the service and the language model are included in the installer; nothing is downloaded later. The edition without AI contains no language model.
• Microsoft Store version: it contains no language model and does not read invoices.
• Reading invoices: when reading in an invoice, the program communicates only with its own bundled service on the same computer (127.0.0.1); it does not use any other service. The invoice does not leave your computer.
• Browser: “Lizenz kaufen” (buy licence) and the notice of a new release open the product page in your browser only when you click.

B 5 System requirements

• Windows 10 build 17763 or later, or Windows 11, 64-bit, with Microsoft’s WebView2 runtime (included in Windows 11; the installer warns if it is missing)
• 73 MB of disk space for the edition without AI; installation does not require administrator rights
• for reading invoices, the AI edition: about 2.7 GB of disk space, the service and the language model are included and no separate Ollama is needed; a graphics card is recommended. The edition without AI does not read invoices with the language model.

B 6 Scope of the licence

The licence applies to one person and their own computers (A 6(2)).

B 7 Access, output and backup

Viewing, preparing statements, printing and exporting are possible even without a licence certificate. The data remains readable as JSON and PDF without this program. The program deletes nothing and has no button for doing so; uninstalling leaves the data folder untouched. You make a backup on another storage medium yourself (A 10(4)).

B 8 Notices of new releases

As long as the version check under B 4 is switched on, the program shows a new release together with a link to the product page. In the Microsoft Store version, the program shows no notices of new releases; the Store handles updates itself.

B 9 Third-party components

reportlab, pywebview, httpx, httpcore, idna and pycparser (BSD-3), anyio, bottle, cffi, charset-normalizer, h11, pythonnet and proxy_tools (MIT or MIT-0 respectively), Pillow (MIT-CMU), typing_extensions (PSF-2.0), cryptography (Apache-2.0 or BSD-3), pypdfium2 with PDFium (BSD-3 and Apache-2.0), clr_loader, certifi (MPL-2.0, shipped unmodified) and the Lexend typeface (SIL Open Font License 1.1). For the licence check in the Microsoft Store, winrt-runtime, winrt-Windows.Foundation and winrt-Windows.Services.Store are added (MIT). The AI edition also contains Ollama (MIT) and the language model qwen3:4b (Apache-2.0).

B 10 Description of performance

10.1 Mietfix calculates and documents. It does not decide.

Mietfix calculates and documents. It does not decide. Whether an item is recoverable from tenants (umlagefähig), whether an agreement is contained in the tenancy agreement, whether a statement is formally valid: these are legal questions and remain with the landlord. The references to the BetrKV, HeizkostenV and BGB are legal sources, not legal advice. No warranty is given for the correctness of a statement.

Nor is it tax or investment advice: the tax in the investment calculator is greatly simplified.

10.2 What “no warranty” means

Mietfix calculates according to the details you enter and the allocation keys you choose. The sentence “No warranty is given for the correctness of a statement” is not a limitation of liability under A 11 or of the rights under A 9, but a description of what the program does: it cannot know what your tenancy agreement says. If the program calculates incorrectly according to its own rules, that is a defect (A 9).

You should therefore check every statement before you send it. For this purpose, the program shows for each item the invoice, the reference in the supporting document, the legal source and the complete calculation. The built-in rules were checked against the official versions of the legislation on 28 September 2026; regulations may have changed since then.

10.3 Twelve-month deadline

The program tracks the deadline for the statement under section 556(3) BGB for each tenant party as a notice and calculates it against the date of receipt by the tenant. Meeting the deadline remains your responsibility. The program knows the date of receipt only if you enter it, and it does not send anything. It does not assess whether you are responsible for a delay.

10.4 Not covered

Condominium owners’ associations (Wohnungseigentümergemeinschaften), statements of owners’ contributions (Hausgeldabrechnungen) and VAT are not covered.

10.5 Change of user without an interim reading

If there is no interim reading at a change of user, Mietfix from version 1.4.5 splits the entire heating costs by time (section 9b(3) HeizkostenV). Mietfix no longer uses degree-day figures.

10.6 Reading invoices with the language model

The optional language model suggests items from invoices. Every item read in this way carries the label “vom Sprachmodell” (from the language model) with the name of the model. No item counts without confirmation by a person; there is no way to set this automatically. No particular hit rate is warranted.

10.7 Profitability

The investment calculator, repayment schedule and household budget book are calculation tools. The tax calculation is greatly simplified. The program does not provide tax or investment advice.