Age calculator
- Runs in your browser
- No signup
- Formula shown below
- Reviewed
An age calculator counts the whole years, then whole months, then remaining days between a date of birth and a chosen date. Someone born on 15 May 1990 is 36 years, 2 months and 25 days old on 9 August 2026, which is 13,235 days in total. The next birthday falls 279 days later, on 15 May 2027.
Defaults to today.
Result
Age on August 19, 2026
36 y 3 m 4 d
whole years → whole months → remaining days, clamped at month ends
- Age in years
- 36
- Age in months
- 435
- Age in weeks
- 1,892
- Age in days
- 13,245
- Age in hours
- 317,880
- Next birthday
- May 15, 2027 (269 days)
- Day of the week born
- Tuesday
Someone born on May 15, 1990 is 36 years, 3 months and 4 days old on August 19, 2026. That is 13,245 days in total, and the next birthday falls in 269 days on May 15, 2027.
How to use the age calculator
- 01
Enter the date of birth
Type or pick the birth date. The calculator accepts any date, including dates in the distant past.
- 02
Set the comparison date
Leave the second field at today for current age, or change it to calculate age at a past or future date — useful for eligibility cut-offs.
- 03
Read the exact age
The result strip shows years, months and days. The rows beneath convert the same period into months, weeks, days and hours.
- 04
Check the next birthday
The rows also show the next birthday date, how many days remain, and which weekday the birth date fell on.
The formula
age = whole years elapsed, then whole months, then remaining days
- whole years
- Complete anniversaries of the birth date that have already passed.
- whole months
- Complete calendar months since the most recent birthday.
- remaining days
- Days since the last whole month boundary, clamped to real month lengths.
- total days
- The exact count of calendar days between the two dates, including leap days.
Month boundaries are clamped, not borrowed. Someone born on 31 January reaches one month of age on 28 February in a common year and 29 February in a leap year, because no 31 February exists. All arithmetic is performed in UTC so a result never shifts with the viewer's time zone.
Worked example
- Date of birth
- 15 May 1990
- Age at this date
- 9 August 2026
- Result
- 36 years, 2 months and 25 days
From 15 May 1990 to 15 May 2026 is 36 complete years. From 15 May 2026 to 15 July 2026 is a further 2 complete months, reaching 15 July 2026. From 15 July 2026 to 9 August 2026 is 25 remaining days. The total elapsed period is 13,235 days, which includes 9 leap days. The next birthday, 15 May 2027, is 279 days after the comparison date.
Frequently asked questions
How is exact age calculated?
Exact age counts complete years from the birth date first, then complete months from the most recent birthday, then the remaining days. This ordering matters: counting total days and dividing by 365.25 gives a decimal approximation, not the calendar age used for legal, medical and administrative purposes.
How is age handled for someone born on 29 February?
A leap-day birth date has no anniversary in common years, so a convention is required. The prevailing legal and administrative treatment in the United States and the United Kingdom recognises 1 March in common years, and this calculator follows that convention. Some jurisdictions and organisations instead use 28 February.
How many days are there in an average year?
The Gregorian calendar averages 365.2425 days per year. Leap years add a day in every year divisible by four, except centuries not divisible by four hundred — so 1900 was not a leap year and 2000 was. That rule keeps the calendar aligned with the solar year to within one day per 3,030 years.
How do you calculate age in months?
Multiply the whole years by twelve and add the whole months. Someone 36 years and 2 months old has lived 36 × 12 + 2 = 434 complete months. Paediatric growth charts and vaccination schedules use age in whole months for the first several years, because monthly resolution matters most when development is fastest.
Does this age calculator work for future dates?
Yes. Setting the comparison date in the future returns the age that will be reached on that date. This is the practical way to check school entry cut-offs, retirement dates, licence eligibility, or minimum age requirements for a scheduled event. The comparison date must fall on or after the birth date.
Why does my age differ by a day in some calculators?
Time-zone handling is the usual cause. A calculator using local time can advance or delay the date boundary by up to a day relative to one using UTC. This calculator performs all arithmetic in UTC, treating a birth date as a calendar fact rather than an instant, so the same inputs always produce the same result anywhere in the world.
Sources
- Leap years and the Gregorian calendar — US National Institute of Standards and Technology
- ISO 8601 — date and time representation — International Organization for Standardization
- Leap seconds and calendar timekeeping — US Naval Observatory
Last reviewed: · Formula and sources verified by Syed Aqeel Ahmad Gillani. See the methodology for how every calculation is derived.