Date Calculator

Birthday Countdown Calculator

Countdown the exact days and weeks until your next birthday, and see what age you will turn.

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100% Private: Your calculation happens entirely inside your browser. Your dates are never stored or transmitted.

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What is the Birthday Countdown Calculator?

The Birthday Countdown tracks how many days, weeks, and days remain until your next birthday, displaying your upcoming age and weekday celebration date.

How to Use This Calculator

  1. Select your birth month and day.
  2. Optionally enter your birth year to compute your upcoming age.
  3. Click Calculate to see the countdown.

Calculation Logic & Formula

Target Birthday is set to this year’s or next year’s anniversary date, and days remaining = toEpochDays(Birthday) - toEpochDays(Today).

Worked Example: Birthday on December 12 as of September 16, 2026

Scenario: Counting down to an upcoming milestone party.

Calculation: September 16 to December 12 is 87 days.

Result: 87 days away (12 weeks, 3 days, on Saturday, December 12, 2026).

Frequently Asked Questions

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