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Date, Time & Productivity

Birthday Countdown.

Dates, holiday lists and durations remain in this browser. Count down to the next birthday and show weekday. Uses explicit date-only Gregorian rules and independent local verification.

Use Birthday Countdown

Private in this browser. Dates, durations and user-supplied holiday lists stay in this browser.

Tool options
Preparing the local tool…

How it works

  1. 01

    Enter dates or elapsed durations and select the rules.

  2. 02

    Run the bounded local calculation.

  3. 03

    Review the calendar rules before downloading the verified result.

Frequently asked questions

Does this use my time zone?

No. Date arithmetic is deliberately independent of time zones and daylight-saving changes.

Does Birthday Countdown upload my data?

Birthday Countdown runs locally in your browser. Dates, durations and user-supplied holiday lists stay in this browser.

What output does Birthday Countdown create?

Birthday Countdown creates Json output after the result passes its local verification checks.

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