Date and Age Calculator

What this tool does

It performs the two date calculations people need most and that are tedious by hand:

• Difference between two dates — how many years, months and days lie between one and the other. It is the operation behind “how old am I?”, “how many days until…?” or “how long have I been doing this?”. Alongside the exact age you get the totals: total days, weeks and months.
• Add or subtract time from a date — starting from a given date, move forwards or backwards by a number of days, weeks, months or years, and find out which date (and which weekday) the result lands on.
• Convert a duration — how many days, weeks, months, hours and minutes “2 years and 5 months” are, or how many months old a 34-year-old is. Gives the exact count from a date and the average that contracts use.

Everything happens in your browser using your local date. Nothing is uploaded and no history is kept.

How to calculate age or days between two dates

1. Leave the mode on Difference.
2. Enter the start date (a date of birth, for example) and the end date (today, or another).
3. Read the result: age in years, months and days, plus the total days, weeks and months.

There is no button to press; the result recalculates whenever either date changes.

Why “2 years and 3 months” is not the same as “820 days”

They are two correct ways of measuring the same interval, and they serve different purposes. Age in years, months and days is what we use for people and anniversaries; it respects the fact that each month has a different length. The total in days is what matters for deadlines, interest or any calculation that needs a single unit. This calculator gives you both at once so you do not have to choose.

How to add or subtract days from a date

1. Switch to Add / Subtract mode.
2. Enter the starting date.
3. Choose the amount and the unit: days, weeks, months or years.
4. Pick whether to add (move forward) or subtract (move back).

The result includes the final date and the weekday it falls on — useful for knowing whether a deadline lands on a weekend.

Typical cases: the cut-off for a “30 days” procedure, an invoice due in 60 days, or when a 2-year warranty period expires.

How old am I, exactly

This is the most frequent query that brings people to this page, and the answer has a nuance almost no calculator explains: your age is not “current year minus birth year”. It depends on whether this year’s birthday has already passed.

Someone born on 20 December 1990, looked at in 2026:

Subtracting years (2026 − 1990 = 36) is only right from the birthday onwards. Before that date it is one year too many. That is the difference between what a subtraction says and what the civil registry says, and in age-gated paperwork — a licence, a grant, a pension — it is exactly the year that decides.

That is why the tool returns years, months and days rather than just the round number.

What year was I born if I am X years old

The inverse operation, with the same nuance. At 32 years old in 2026 there are two possible answers and the right one depends on the month:

• If your 2026 birthday has already passed: you were born in 1994 (2026 − 32).
• If your birthday has not arrived yet: you were born in 1993 (2026 − 32 − 1).

Without knowing the month, the subtraction alone leaves you with two candidate years. The safe way to settle it is backwards: put the birth date you believe is right into Difference mode against today’s date and check which age it returns. If it is the one you expected, that is the one.

How many days are 2 years and 5 months (and why there are two answers)

It is the other question that brings people here, and the short answer is 883 days on average. The long answer is that a duration in years and months has no fixed number of days until you say which date you count from, because months run from 28 to 31 days and every four years there is a 29 February:

That is why Convert duration mode gives you both: the exact count from the date you pick (today by default), and the average, which is what you use when there is no specific date: contract terms, interest, warranties. If someone asks “how many days are 3 years and 7 months” for a legal calculation, the average is the expected answer; if it is to know when something expires, count from the real date.

Type the duration into the years, months, weeks and days fields and the days, weeks, months, hours and minutes appear below. The four boxes combine: “1 year, 2 months and 10 days” is the same as “14 months and 10 days”.

How many months old is a 34-year-old

408 months: completed years times twelve. A 35-year-old is 420 months old and a 36-year-old 432. It is the figure medical and paediatric forms ask for, where age is requested in months, and duration mode shows it directly when you type only the years.

Days are a different story: 36 years are 13,149 days on average, but between 13,148 and 13,150 exactly depending on how many 29 Februaries fall in the span. If you need the exact number for a specific person, use Difference mode with their birth date; if you need the generic conversion, use duration mode.

The details that usually cause errors

Does the final day count or not?

The difference is computed as complete days elapsed, without counting the final day. From 1 to 10 March there are 9 days of difference, not 10. If what you are counting is occupied days — hotel nights, rental days, holiday days — you almost always want both ends included: add 1 to the total.

Months are not all the same length

Adding “1 month” to 31 January cannot give 31 February, because it does not exist. Just as in spreadsheets and programming languages, the result is clamped to the last valid day of the target month. That is why month jumps are worth checking when the starting day is the 29th, 30th or 31st.

Leap years

The calculation uses the real calendar, so 29 February counts. Someone born on 29 February has a birthday every year, but their exact birth date only comes back every four. The calculator handles both dates without inventing a day that does not exist.

Time zones

Everything is computed with your local date, with no times and no zone conversion. That is the correct approach for counting calendar days: mixing time zones is exactly what produces the “one day off” error in many online calculators.

Questions it answers

• How many days until a date? → Difference mode between today and that date.
• How old is someone born on a given date? → Difference between the birth date and today.
• What date falls 90 days from now? → Add mode, 90 days.
• How many weeks into the project am I? → Difference, look at the total weeks.
• What weekday will a given date be? → Add mode gives you the weekday of the result.
• How many days are 2 years and 5 months? → Convert duration mode, exact from a date plus the average.
• How many months old is a 34-year-old? → Convert duration with only the years: 408.
• How many hours are 3 weeks? → Convert duration, look at the hours: 504.