Age Calculator · Years, Months, Days, Next Birthday
Enter a birth date to instantly compute exact age in years/months/days, Chinese nominal age, total days/hours lived, days to next birthday and zodiac sign. All computed locally.
Overview
It's surprisingly easy to lose track of your exact age between birthdays. This tool instantly shows your precise age down to the day, Chinese nominal age, total days and hours lived, countdown to your next birthday, and zodiac sign. Everything is computed locally in your browser — no data leaves your device.
How to use
- Pick your birth date (any date between 1900-01-01 and today).
- The reference date defaults to today; adjust it to compute age on any past or future date.
- Results show exact age, nominal age, total days, days to next birthday and zodiac.
Formula
1) Exact age: years/months/days via borrow-carry on calendar fields. 2) Chinese nominal age: reference_year − birth_year + 1. 3) Total days: floor((ref_utc − birth_utc) / 86_400_000). 4) Days to next birthday: construct the next birthday date (handling Feb 29 by rolling to Feb 28 in non-leap years) and diff in UTC days.
Common scenarios
Scenario 1 · Before vs after birthday
Your age ticks up exactly on your birthday, not before. This tool shows the precise boundary at any day, no rough "divide by 365" tricks.
Scenario 2 · Feb 29 birthdays
In non-leap years the next birthday rolls to Feb 28 so you don't skip a year.
Scenario 3 · Age on a historical date
Change the reference date to compute your age on any past or future day.
FAQ
What is the difference between "real age" and "nominal age"?
Real age increments on each birthday. Chinese nominal age treats the birth year as year 1 and adds 1 each new year — this tool uses the simple "year_diff + 1" rule. Use real age for any legal or official form.
Why compute days via UTC?
Using UTC midnights avoids DST and timezone offsets causing off-by-one errors. Integer-day results are exact; sub-day precision isn't the goal.
How are Feb 29 birthdays handled in non-leap years?
This tool treats Feb 29 as Feb 28 in non-leap years when computing the next birthday. Choose any convention you like for the actual celebration.
Does it support lunar-calendar age?
Not yet — only Gregorian calendar. A lunar-calendar variant is planned.
Does this tool upload my birthday?
No. All calculations run locally in your browser; no data leaves your device.
How is zodiac determined?
Uses the standard Gregorian zodiac date ranges. Note edge cases (±1 day) vary by astrology source.
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