Age Calculator
Years, months, days, weeks, and total days lived from a date of birth.
Calculator
Enter your date of birth above to see your age.
How it works
The calculator subtracts the date of birth from today using the relativedelta algorithm, which is the standard approach in scientific date libraries. It first computes the raw difference in years, months, and days, then borrows from the next-larger unit when a component goes negative. For example, a birthday of March 5 to a reference date of April 2 first computes 0 years, 1 month, -3 days; because days are negative, it borrows 31 from April-prev-month March, giving 0 years, 0 months, 28 days. The total day count is computed separately as the absolute floor difference in 24-hour periods, and weeks lived is total days divided by seven.
Why use this calculator?
Age in years alone is too coarse for many real-world questions. Insurance premiums often change at exact age thresholds, school enrollment cutoffs are tied to specific dates, and pediatric developmental milestones are tracked in months for the first few years. Knowing age in days and weeks is also surprisingly meaningful for milestone moments — many parents track infant age in weeks for the first half-year, and many people enjoy seeing their cumulative days lived as a personal milestone count.
FAQ
Why does my age sometimes look one day off?
The calculator uses UTC and ignores time-of-day. If you live in a time zone that is several hours behind UTC and load the page near midnight UTC, the displayed today date may briefly disagree with your local clock. The next day this resolves automatically.
How is age handled for someone born on February 29?
In leap years they age on February 29 as expected. In non-leap years they age on March 1 — which is the convention used by most legal systems, software libraries, and birthday-tracking apps. So a person born February 29, 2000 turns three on March 1, 2003.
Why are weeks lived not just total days divided by seven exactly?
They are exactly that, rounded down. If you have lived 365 total days, weeks lived is 52, because 52 × 7 is 364 and the 365th day has not yet completed a 53rd week. The display is intentionally a whole number for easier mental anchoring.
Can I calculate age as of a date other than today?
This calculator anchors to today. If you need to compute age as of a historical or future date, use the Days Between Dates calculator with the date of birth and the reference date — it returns the day count, and you can convert that to years and months mentally or use the formula in the explainer above.
Is my date of birth stored anywhere?
No. The math runs in your browser, and the only place the date appears outside your browser is the URL of this page — which never leaves your device unless you copy or share it. There is no analytics call, no server-side log of inputs, and no third-party tracker on the page.