Age in Years Calculator
Get both calendar age (years, months, days) and decimal years—ideal for HR forms, educational placement, or personal records.
Use today by default or select any comparison date.
Birth: 1/1/1990, 12:00:00 AM
Reference: 11/25/2025, 11:49:00 AM
Calendar age: 35 year(s), 10 month(s), 24 day(s)
Decimal years: 35.900048
Total months: 430.8006
Total days: 13112
How to Use This Calculator
Enter birth/start timestamp
Include the exact date and time if available.
Select reference timestamp
Use now or any future/past comparison date.
Copy the results
Record age in calendar format or decimal years for forms and reports.
Formula
Decimal Years = (Reference − Birth) ÷ (365.25 × 24 × 3600 × 1000)
Calendar Age = Year/Month/Day difference with month-length adjustments
Total Months = Decimal Years × 12
Example: 1990-01-01 → 2025-11-09 = 35 years, 10 months, 8 days → 35.851 years.
Age-Based Planning Ideas
- Confirm eligibility for programs with age limits (education, sports, pensions).
- Convert ages to decimal years for actuarial or financial modeling.
- Plan milestone celebrations (e.g., 40th birthday) precisely.
- Align marketing or product messaging with customer age cohorts.
Frequently Asked Questions
Why use 365.25 days for decimal years?
It accounts for leap years on average, offering a standard conversion widely used in finance and science.
Can I ignore the time of day?
Set both times to midnight to focus on calendar dates only.
What if I need a birth certificate style output?
Use the Age in Years, Months, and Days calculator for more detailed breakdowns.
Does timezone affect results?
Calculations use your local timezone. To compare across zones, convert inputs to the same timezone first.