About this calculator
Figuring out an exact age — down to the month and day, not just the year — comes up for forms, eligibility rules, and milestone planning more often than you'd expect. This calculator takes a birth date and a reference date (defaulting to today) and returns the precise age in years, months, and days, along with the total number of days you've been alive.
How it works
The calculator finds the difference between the two dates and breaks it down into whole years, remaining whole months, and remaining days — accounting correctly for varying month lengths and leap years, which is where doing this kind of date math by hand most often goes wrong.
Worked example
Someone born May 15, 1990, checking their age as of September 7, 2026, is exactly 36 years, 3 months, and 23 days old — 13,262 days in total.
Frequently asked questions
Why does the calculator need an "as of" date?
Defaulting to today gives your current age, but entering a future or past date lets you work out how old you'll be (or were) on a specific date — useful for eligibility rules tied to a cutoff date.
Does this account for leap years?
Yes — because the calculation works from actual calendar dates rather than assuming every year has exactly 365 days, leap years are handled automatically and correctly.
Can I use this for something other than a person's age?
Yes — the same date-difference math works for anything measured from a start date, such as how long a project, marriage, or lease has run.
Last reviewed: September 2026.