A Retirement Countdown And The Lessons Of Building With AI

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Developer Thorsten Meyer says he built and released Altersteilzeit, a free web app for people counting down a German partial-retirement schedule, in five days with help from Claude Opus 5.5. The project grew from a request for a one-minute animated film into a site with a working-day countdown, a narrator, and 19 3D games; Meyer says he directed the work and made the decisions about what to release.

Meyer’s account, published October 13 on ThorstenMeyerAI.com, dates the initial request to Monday, September 28, 2026, and the release to Friday, October 2. Altersteilzeit is a form of partial retirement in Germany. In the block model, a person works through an active phase and then spends an equivalent period away from work in a passive phase. The app supports models from 1:1 to 5:5, according to Meyer.

Users enter the start date of either phase. The app then calculates the other date and remaining working days, accounting for weekdays, public holidays in the user’s German federal state and entered leave. Its features include a daily countdown and milestones, a short narrated film, games organized around the years of the active phase, a team countdown, a bridge-day finder, badges and calendar tools. Meyer describes seven languages and five German dialects in the finished product.

Meyer says every one of the project’s 24 commits was co-authored by the coding agent. He reports that the work included about 18,000 lines of JavaScript and Python, 15 test scripts, and 1,224 voice clips. These figures and descriptions come from Meyer’s account; the source material does not provide an independent technical audit. He says the app calculates dates in the browser and has no accounts, cookies or tracking.

What the Five-Day Build Shows

The project offers a specific account of how a developer used an AI coding agent across a small product’s development and release, rather than relying on a single demonstration of code generation. Meyer describes using the agent for engineering, translation, audio production and deployment, while he supplied the idea, tone and release decisions. That division of work matters to readers weighing AI tools: the account presents speed alongside the human review that still shaped the result.

The app also shows how a personal need can drive a broader product. A countdown for a particular retirement schedule became a set of utilities and games built around calendar time. For people using the German block model, the practical value is the calculation of working days and local holidays; the film and games are optional ways to make the wait more engaging. The source does not report user numbers, independent testing or evidence that the app’s calculations have been verified by an outside party.

From Film to Calendar Tool

The project began with a narrow request: a short animated film counting down working days in an Altersteilzeit block model. Meyer says the app expanded over five days and 24 commits, with features added in successive rounds. The first day brought the film, date calculations and game prototypes; later days added languages, the daily view, more games, badges, a bridge-day finder, narration and sound effects. Meyer says he approved the release on the fifth day.

The game design uses calendar units as game mechanics, according to Meyer. For example, one game maps columns to months and cells to weeks, while another treats each email as a working day. The reported build also includes legal pages for a public website. Meyer says dates shared through a link are stored after the “#” in the address, which browsers do not send to servers, and that calculations take place locally. Those privacy details are the author’s description, not a separately reported security assessment.

“The interesting part is not how much an AI agent can build, but what was still left for me to do.”

— Thorsten Meyer, writing on ThorstenMeyerAI.com

Independent Checks Still Missing

The available source is Meyer’s own account of building and releasing the app. It does not include independent confirmation of the development timeline, commit history, reported code volume, test coverage or number of voice clips. It is also not clear from the material how many people have used the app, whether its date calculations have been reviewed by specialists, or whether the reported privacy safeguards have undergone an external security assessment.

The source says the app was online by October 2, but provides no separate link or verification of its current availability. Meyer’s description of AI contributions also does not specify how much of the generated code or other output required revisions, beyond mentioning a fix for a mobile scrolling problem.

Availability and Verification

Meyer’s account describes Altersteilzeit as a free public web app, but the supplied material gives no announced follow-up release, user data or external review schedule. Readers seeking to use it can check the site named in the account for current availability and product details. Any further claims about reliability, privacy or adoption would need evidence beyond the author’s project report.

The next useful measures would be independent checks of the date calculations and privacy behavior, alongside information about actual use and maintenance. Until such details are available, the five-day timeline and technical totals should be treated as Meyer’s reported figures, while the broader lesson is his account of AI assistance working alongside human direction and approval.

Key Questions

What is Altersteilzeit?

Altersteilzeit is a German partial-retirement arrangement. In the block model described by Meyer, a person works during an active phase and then has a corresponding passive phase away from work.

What does the app calculate?

Users enter the start date of one phase and choose a schedule model. The app calculates the other date and remaining working days, using weekdays, the selected German federal state’s public holidays and leave entered by the user, according to Meyer.

How did AI contribute to the build?

Meyer says Claude Opus 5.5 assisted with coding, testing, translations, audio assets and deployment. He says he provided direction, made product and creative decisions, and approved releases.

Has the app been independently verified?

The source material does not report an independent audit of the app’s calculations, code, privacy protections or security. The technical details in the account are attributed to Meyer.

Source: ThorstenMeyerAI.com