Reference formulas and worked examples below keep their stated units. Monetary examples use USD; dimensional examples use US customary units unless labeled otherwise. Metric calculator inputs are converted to these reference units before calculation. Choosing another currency does not convert example amounts or exchange money.
How to use this age calculator
Choose an age calculation or an age gap. For a gap, enter both birth dates in either order; the result identifies the older person.
How the calculation works
Find the largest completed number of calendar months from the birth date. When the destination month lacks the birth day, use its last day.
Split completed months into years and months. Count remaining days from that month anniversary to the selected date.
Total days are the exact date-only difference. Leap days count, while time of birth and time zones do not affect this date-only calculation.
Age difference applies this same elapsed-calendar calculation from the earlier birth date to the later one. Input order changes the older-person label, not the size of the gap.
Worked example
From June 15, 1990 to September 22, 2026, there are 36 years, 3 months, and 7 days. A birth date of February 29, 2024 reaches one year on February 28, 2025 under this tool’s month-end convention. Two birthdays of June 15, 1990 and September 22, 1995 are 5 years, 3 months and 7 days apart.
Limits and assumptions
Uses the Gregorian calendar, years 1000–9999. Month-end anniversaries are clamped to the last day available. This is a calendar convention; legal birthday rules can differ.
Frequently asked questions
Can I compare two people?
Yes. Choose Age difference and enter both birthdays. Reversing them preserves the difference and switches the older-person label.
How are leap-day birthdays counted?
February 29 becomes February 28 in a non-leap year under this calculator’s explicit month-end convention.
Why do some age calculators give a different number of days?
Tools can use different conventions for anniversaries near month ends. This tool counts full clamped calendar months first, then the remaining days.
Can I calculate an age on a future date?
Yes. Enter the future date in Age on date.