Age Calculator
Enter your date of birth and (optionally) an as-of date to see your precise age with steps and a clean final result.
Your dates
Final age result
Results interpretation
- Exact components: The breakdown in years, months, and days is calendar-accurate and accounts for different month lengths.
- Totals: Days, weeks, and months are helpful for milestones and eligibility checks.
- Who it’s for: Students, HR/onboarding, insurance cutoffs, sports leagues, and birthday/event planning.
How this calculator works
We compare two calendar dates, borrow days and months where needed, and normalize to a years–months–days triple. Totals are derived from the exact day count.
Show math & assumptions
- Let
dobandasOfbe dates at local noon to avoid DST edge cases. - Base differences:
Y=Δyears, M=Δmonths, D=Δdays. - If
D < 0, borrow from previous month:M -= 1,D += daysInPrevMonth. - If
M < 0, borrow from years:Y -= 1,M += 12. - Total days:
⌊(asUTC − dobUTC) / 86400000⌋using midnight UTC. - Feb 29 birthdays: next birthday falls on Feb 28 in non-leap years.
FAQ
How accurate is the age in months and days?
It’s calendar-accurate, borrowing days from the previous month and accounting for month length and leap years.
What if I was born on February 29?
We map the next birthday to Feb 28 in non-leap years so your countdown remains meaningful.
Does time of day matter?
No—this tool uses dates only. For hour-level precision, use a time-aware age tool.
Why does my “days old” differ from another site?
Different tools may treat end-points inclusively or exclusively. We use UTC day boundaries for consistency.
Can I change the as-of date?
Yes—pick any date to compute age at that moment (e.g., eligibility checks).
Will switching time zones change results?
No. We compute using calendar dates, not times; day counts are stable.
Use cases & examples
- Eligibility: Check “at least 18 years old on 2027-08-01” by setting As-of to that date.
- Milestones: Find weeks or days until a birthday or anniversary.
- Project timelines: Convert months to exact days for contracts or benefits.
What this Age Calculator does
Age calculator tools help you convert a birth date to an exact, human-readable age in years, months, and days. This page is built for clarity: you type dates, and it instantly shows the math and a clean final answer. It also displays total days and weeks lived, your next birthday, and a countdown to that date.
Why precise age matters
Legal eligibility, school placement, sports divisions, and benefits often hinge on a specific cutoff date. A calendar-accurate result prevents off-by-one errors that can occur when months are assumed to equal 30 days or when leap years are ignored.
How to use this tool
Enter your date of birth. The as-of date defaults to today but can be changed for future or past checks. The amber steps summarize the borrowing process used to compute months and days; the green banner presents the final age.
Behind the scenes
The calculator compares calendar fields and borrows when needed—if the as-of day is less than the birth day, it borrows from the previous month, then normalizes months within 0–11. This mirrors how people explain age in everyday language while remaining fully deterministic.
Common pitfalls
- Assuming all months have 30 days.
- Ignoring leap years, which can shift totals by a day.
- Mixing time-of-day into a date-only calculation and getting DST artifacts.
Limitations
This is a date-only calculator. If you need to include times and time zones, use a full datetime calculator. For Feb 29 birthdays, conventions vary; we pick Feb 28 in non-leap years for the next-birthday countdown.
Practical examples
Example 1: DOB 2001-03-15, as-of 2025-08-18 → 24 years, 5 months, 3 days; next birthday 2026-03-15.
Example 2: DOB 2012-02-29, as-of 2025-08-18 → leap handling applies; next birthday maps to 2026-02-28.
Example 3: Eligibility check—set as-of to the policy date and confirm whether the age meets the requirement on that day.