Age Calculator Between Two Dates
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This age calculator between two dates measures the exact gap from a start date to an end date in years, months and days. Put a birth date in the first box and any later date in the second, and it tells you how old a person was or will be on that day. Put two ordinary dates in instead, such as a hire date and today, and the same math gives you a precise duration.
The tool also returns the gap as total months, weeks and days, and it can count the end date or leave it out. That one checkbox explains most of the one day differences people notice when they compare tools. Results follow the Gregorian calendar, so leap days and months of different lengths are handled for you.
How to Use the Age Calculator Between Two Dates
Enter the earlier date as the start date and the later date as the end date, using month, day and year order. Press Calculate and the main result appears as years, months and days, with the totals listed underneath it. If you enter the dates in the wrong order, the tool swaps them and shows the same span instead of a negative number.
Leave the include end date option unchecked when you want age or elapsed time, because that is how ages and anniversaries are counted. Tick it when you are counting calendar days that each matter, such as nights of a hotel booking or days of a medication course. With the box ticked, the total grows by exactly one day and nothing else changes.
When to tick include end date
Ages and birthdays
Time since a hire date
Interest and notice periods
Chronological age for testing
Nights or days of a booking
A course of medication
Festival or event days
Leave counted by calendar day
Find Your Age on a Specific Date
Most people use this age calculator between two dates to answer one question: how old was I, or someone else, on a particular day. A birth date of May 9, 1985 and an end date of September 11, 2001 gives 16 years, 4 months and 2 days, which is how old that person was on that morning. The same approach works for future plans, such as checking how old a child will be on the first day of kindergarten.
Ages tied to a fixed date come up more often than you might expect. Little League baseball measures age on August 31, scholarship and exam forms ask for age on a stated date, and some visa applications do the same. In each case, enter the cutoff as the end date rather than today, since the result has to match the date written in the rules.
How the Time Between Two Dates Is Calculated
The age calculator between two dates counts forward from the start date in whole years first, then whole months, then the days that are left. A month counts as complete when the end date reaches the same day number in a later month, so March 10 to April 10 is one month even though it spans 31 days. Whatever remains after the last full month becomes the day count.
Total days are worked out separately by turning both dates into a serial day number and subtracting one from the other. Astronomers use the same idea with the Julian day number, and spreadsheets do it with date serials, which is why Excel returns 365 for two dates exactly one common year apart. Total weeks are the total days divided by seven, with the remainder shown as extra days.
- StartMay 9, 1985
- Add 16 yearsMay 9, 200116 years
- Add 4 monthsSeptember 9, 20014 months
- Count the restSeptember 11, 20012 days
Need the total as years only?Turn any day count into years, months and weeks with the days to years converter.
Convert daysInclusive vs Exclusive Counting
Exclusive counting treats the start date as day zero, so January 1 to January 2 is one day. Inclusive counting treats both dates as full days, so the same span becomes two days. Ages, interest periods and most legal deadlines use exclusive counting, while event schedules and some leave policies use inclusive counting.
Pearson, one of the largest test publishers, sends its users to a date duration tool with a specific instruction not to tick the include end date box. That instruction exists because the extra day can push a child’s chronological age into the next month and change which norms table applies. When in doubt, leave the box unchecked in the age calculator between two dates and the result will match how age is normally counted.
Ages, interest, legal deadlines
Event schedules, some leave rules
Frequently Asked Questions
How do I calculate the time between two dates?
Count the full years from the start date, then the full months, then the remaining days, in that order. The age calculator between two dates does this instantly and also gives the total number of days. For a rough day count by hand, multiply the years by 365.25 and add the extra months and days.
Does the calculation include the end date?
By default it does not, because ages and elapsed time are counted from day zero. Tick the include end date box if every calendar day in the range should count, such as the days of a festival. Doing so adds exactly one day to every total.
How old was I on a specific date?
In the age calculator between two dates, enter your date of birth as the start date and the day you are curious about as the end date. The years, months and days result is your exact age on that day. It is the same figure a school, a sports league or an exam board would use for age as of a cutoff date.
How many days are there between two dates?
Subtract the earlier date’s day number from the later one, which is what the total days line shows. Across a full common year the answer is 365, and across a year containing February 29 it is 366. Spreadsheet programs give the same result when you subtract one date cell from another.
Why do two calculators give different results for the same dates?
The usual causes are the include end date setting and different rules for start dates near the end of a month. One tool may count January 31 to February 28 as a full month while another counts it as 28 days. Check both settings and the results normally line up.