"How old are you?" sounds like an easy question. "24." But the precise answer — 24 years, 7 months, 12 days — is harder than it looks, because months have unequal lengths and Februaries have leap years. Here's how it's done.
Open the Age Calculator to compute yours.
The algorithm
- Compute the difference in years between today and the birth date.
- If today's month/day hasn't yet reached the birth month/day this year, subtract 1.
- Compute the difference in months similarly within the partial year.
- Compute the difference in days similarly within the partial month, accounting for the actual length of the previous month.
JavaScript's Date object handles steps 2–4 if you decompose carefully. The calculator also handles:
- Leap years (Feb 29 birthdays show "next birthday in N days" correctly)
- Time zones (always computed in the user's local zone)
- DST transitions (irrelevant since the math is in days, not hours)
Use cases beyond birthdays
| Use case | Why an age calc |
|---|---|
| HR forms | Exact tenure / age for compliance fields |
| School admissions | "Child must be 6 years 0 months by April 1" — calculate cutoff |
| Insurance / actuarial | Premium tiers shift at exact day boundaries |
| Pet age | Convert dog/cat age to "human equivalent" (separate tool) |
| Anniversaries | "How long since we got married?" |
| Document validity | Passport, visa, license expiry windows |
What the result tells you
CalcMaster's Age Calculator returns:
- Years, months, days (the canonical answer)
- Total days ever lived
- Total weeks ever lived
- Days until next birthday
- Day of the week you were born (small but charming)
The leap-year footnote
Roughly 1 in 1,461 people is born on Feb 29. CalcMaster handles their birthdays by celebrating on Feb 28 in non-leap years (the convention used by the Indian government and most insurance providers). If you'd prefer March 1, that's a one-line settings change we can add — email feedback.
Run yours
Open the Age Calculator and find out how many Tuesdays you've lived through.
