Exact age from a date of birth in years, months and days on any date, with the next birthday and age in months, weeks, days and hours.
By AdminDrafted with AI writing toolsUpdated Checked examples: 4
On Thu 12 Nov 2026 someone born on Sun 20 May 1990 is 36 years, 5 months, 23 days old: 13,325 days in all. Their next birthday is Thursday, 20 May 2027, in 189 days.
The last birthday on or before Thu 12 Nov 2026 is Wed 20 May 2026, so the age is 36 years.
5 whole months from Wed 20 May 2026 reach Tue 20 Oct 2026, then 23 days reach Thu 12 Nov 2026.
Months are counted on the birthday's day of the month; when that day doesn't exist (the 31st in a 30-day month, 29–31 in February), the month's last day is used.
Thu 20 May 2027 is a Thursday, 189 days away; the age then is 37.
Age in years is the number of birthdays reached on the chosen date, following the rule of section 9 of the Family Law Reform Act 1969 (England and Wales) that a person attains an age at the start of the anniversary of their birth. The months and days after that are counted forward from the last birthday: whole months first, then the days left over. Totals in days, weeks and hours come from subtracting the two dates' day numbers.
Forms often ask for age on a fixed date, such as the start of a school year, a competition's cut-off or a pension date, rather than today. Someone born on 20 May 1990 was 35 years, 7 months and 26 days old on 15 January 2026, or 13,024 days, and their next birthday fell on Wednesday, 20 May 2026.
For people born on 29 February, pick whether the birthday counts as 28 February or 1 March in common years; the choice changes the age in whole years only on 28 February of a common year.
Your age is the number of birthdays you have reached. Take your birth year from the current year, and if this year's birthday is still ahead, the answer is one less: someone born on 20 May 1990 is 35 on 19 May 2026 and 36 from 20 May.
Exact age adds the whole months since the last birthday, counted on the birthday's day of the month, then the days left over. When that day doesn't exist in a month, such as the 31st in a 30-day month, the month's last day stands in.
You need the full date of birth: a birth year alone gives two possible ages until you know whether the birthday has passed.
"Age as on" or "age as of" a date is your age on that reference date rather than today. Job and exam applications, school admissions and sports age groups often fix such a date; use it, not the day you apply.
For someone born on 20 May 1990, the age around the 2026 birthday is:
| Age on | Completed years | Exact age | Total days |
|---|---|---|---|
| 19 May 2026 | 35 | 35 years, 11 months, 29 days | 13,148 |
| 20 May 2026 | 36 | 36 years, 0 months, 0 days | 13,149 |
| 21 May 2026 | 36 | 36 years, 0 months, 1 day | 13,150 |
The completed years go up on the birthday itself, not on 1 January.
Your next birthday is the next anniversary of your birth date on or after the reference date. For someone born on 20 May 1990, measured on 21 May 2026, it is 20 May 2027, 364 days away; measured on 20 May 2026, it is that same day. To count down to another event, use the countdown calculator.
Write the date you are measuring on above the date of birth, as year, month and day, and subtract from the right. For someone born on 28 November 1984, measured on 9 March 2026:
The age is 41 years, 3 months and 9 days. Counting forward gives the same answer: the last birthday was 28 November 2025, three whole months reach 28 February 2026, and nine more days reach 9 March. That is 15,076 days, or 2,153 whole weeks.
Borrowing fails when the day of birth is larger than the month you borrow from. Born on 31 January 1990 and measured on 1 March 2026, the day column gives 1 + 28 − 31 = −2 days.
Counting forward has no such gap. One month after 31 January 2026 is 28 February, the last day of that month, and one more day reaches 1 March: 36 years, 1 month and 1 day. On 28 February the age was 36 years, 1 month and 0 days.
Python's dateutil library gives the same answers. Excel's DATEDIF does not always: Microsoft's DATEDIF page says its "MD" unit "may result in a negative number, a zero, or an inaccurate result". Its "Y" unit returns complete years and has no such warning.
The month-end rule matters for babies too: a baby born on 31 August turns one month old on 30 September, because September has no 31st.
Total days come from counting calendar days, not from multiplying years by 365, so every 29 February in the span adds a day. Someone born on 15 February 2008 turns 18 after 6,575 days, because 29 February 2008 falls inside the span; someone born on 15 March 2008 turns 18 after 6,574.
Weeks are whole weeks (days ÷ 7, rounded down). Months are 12 per year plus the months since the last birthday. Hours are days × 24 from midnight at the start of the birth date, so someone born at 18:00 has lived 18 hours fewer than that total.
| Age on the birthday | Months | Days | Whole weeks | Hours |
|---|---|---|---|---|
| 1 | 12 | 365 or 366 | 52 | 8,760 or 8,784 |
| 10 | 120 | 3,652 or 3,653 | 521 | 87,648 or 87,672 |
| 18 | 216 | 6,574 or 6,575 | 939 | 157,776 or 157,800 |
| 21 | 252 | 7,670 or 7,671 | 1,095 | 184,080 or 184,104 |
| 30 | 360 | 10,957 or 10,958 | 1,565 | 262,968 or 262,992 |
| 40 | 480 | 14,610 | 2,087 | 350,640 |
| 50 | 600 | 18,262 or 18,263 | 2,608 or 2,609 | 438,288 or 438,312 |
| 65 | 780 | 23,741 or 23,742 | 3,391 | 569,784 or 569,808 |
An age that is a multiple of 4, such as 40, has a single day count, because any 4 whole years contain exactly one 29 February. That holds between 1901 and 2099; 2100 is not a leap year, so a span including February 2100 has one day fewer. The leap year checker shows which years qualify.
In the Gregorian calendar, 97 of every 146,097 days are 29 February, so if births were spread evenly, about 1 person in 1,506 would have a leap-day birthday. Ignoring the century rule gives 1 in 1,461.
Which date counts as the birthday in a common year depends on where you live, and only some legal systems say:
| Jurisdiction | When the new age starts in a common year | Source |
|---|---|---|
| Scotland | 1 March | Age of Legal Capacity (Scotland) Act 1991, s.6 |
| England and Wales | Not stated; an age is reached at "the commencement of the relevant anniversary of the date of his birth" | Family Law Reform Act 1969, s.9 |
| Japan | The year of age ends with 28 February, so the new age applies from 1 March | Act on Calculation of Age (1902), applying Civil Code art. 143 |
The choice matters most for ages that carry legal rights. Someone born on 29 February 2008 turns 18 in 2026, a common year: on Saturday 28 February under a 28 February rule, or on Sunday 1 March under the Scottish 1 March rule.
Japan's rule has a second effect. A year of age there ends at the close of the day before the birthday, so a child born on 1 April reaches six on 31 March.
The School Education Act, art. 17 starts compulsory schooling in the first school year after a child reaches six, and Japanese school years begin on 1 April. Children born on 1 April therefore start school a year earlier than those born on 2 April of the same year.
Korea has used three counts and China a fourth, and they can differ by two years for someone born late in December. For a person born on 15 December 2005, measured on 10 January 2026:
| Count | How it works | Age |
|---|---|---|
| International age (man nai) | Birthdays reached; what this calculator shows | 20 |
| Year age (yeon nai) | Current year minus birth year | 21 |
| Korean counting age | 1 at birth, plus 1 every 1 January | 22 |
| Chinese nominal age (xusui) | 1 at birth, plus 1 at each Lunar New Year | 21, then 22 from 17 February |
Korea's Civil Act, art. 158 counts age in full years including the day of birth, but some laws keep year age. The Youth Protection Act, art. 2, defines a minor as under 19 but excludes anyone who has reached 1 January of the year they turn 19.
Everyone born in 2007 could therefore buy alcohol and tobacco legally from 1 January 2026, even at 18. For the timing of service duties, the Military Service Act, art. 2, reads "from age X" as from 1 January of the year a person turns X.
Chinese nominal age moves at Lunar New Year rather than 1 January. The Hong Kong Observatory's 2026 calendar table puts the first day of the first lunar month on 17 February 2026.
Japan's Act on Age Counting, in force from 1 January 1950, made full-year age the norm in place of counted age, kazoedoshi. Public bodies must give ages in full years, or in months under one year, and must flag any exceptional use of counted age.
For a span that isn't measured from a birth, such as the days between two events, use the days between dates calculator. The day of the week calculator shows which weekday a date of birth fell on.
Checked against: Independent calculation
Checked against: Rule applied by hand: the 2025 birthday is 28 Feb 2025, so the 25th birthday is reached
Checked against: Rule applied by hand: last birthday 29 Feb 2024; 11 months reach 29 Jan 2025, then 30 days
Checked against: Independent calculation
Subtract your birth year from the current year, then take off 1 if this year's birthday hasn't arrived yet. For the months, count whole months from your last birthday, then the remaining days. Born 20 May 1990 and measured on 15 January 2026, that is 2026 − 1990 − 1 = 35 years, then 7 months to 20 December and 26 days to 15 January.
Subtract your date of birth from today's date as day numbers; leap days are included automatically. Someone born on 20 May 1990 was 13,024 days old on 15 January 2026. The 10,000-day mark comes at 27 years, 4 months and 15 days (5 October 2017 for that birth date), and 20,000 days at about 54 years and 9 months.
It depends on the rule used. Hong Kong's Age of Majority (Related Provisions) Ordinance, section 5, and Scotland's Age of Legal Capacity (Scotland) Act 1991, section 6(2), fix it at 1 March in years that are not leap years. Section 9 of the Family Law Reform Act in England and Wales does not specify an alternative date for 29 February, and many people celebrate on 28 February. Under the 1 March rule someone born on 29 February 2000 was still 24 on 28 February 2025; under the 28 February rule they had turned 25.
Traditional Korean age counts 1 at birth and adds a year every 1 January, so it runs 1 or 2 years ahead of international age. South Korea made international age the general rule for legal and administrative matters on 28 June 2023, with exceptions under specific laws. Someone born in 1990 is 37 in traditional Korean age throughout 2026 (2026 − 1990 + 1), while this calculator gives their international age, 35 or 36 depending on the date.
This calculator includes 4 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.