Date & Age Calculators

Free, instant date and age math that runs entirely in your browser.

Age Calculator Type your date of birth and see your exact age in years, months, days and more. Date Difference Calculator Pick two dates and get the exact days, weeks, months or years between them. Add or Subtract Days from a Date Add or subtract days, weeks, months or years from any date and get the new date. Business Days Calculator Count working days between two dates, excluding weekends and optional public holidays. Countdown Calculator Count down days, hours, weeks until a future date, or count days since a past date. Day of Year & Week Number Calculator Find the day number of the year and the ISO 8601 week number for any date. Birthday Calculator See your next birthday countdown, the day of week it falls on, and your zodiac sign.

DateKit is a small collection of free calculators for everyday date math. Every tool runs on your own device, so the dates you type never leave your browser. There is no account to create and nothing to install — open a tool, type your dates, and read the result.

Below you will find seven focused calculators. Each one solves a single, common question: how old am I, how many days are between two dates, what date is 30 days from today, how many business days until a deadline, how long until an event, what day of the year is it, and when is my next birthday. They share one engine built on the standard Gregorian calendar, so leap years, month lengths and weekends are all handled the way a wall calendar would.

Pick the tool that matches your question. If you are not sure which one you need, start with the age calculator or the date difference calculator — they cover most everyday cases.

How to use DateKit

All DateKit tools use the same underlying date engine. A date is just a point on the calendar; the calculators measure the gap between points using exact midnight-to-midnight counting, not rough estimates. That means a leap year with its extra February 29 is counted correctly, and a month that is 30 days long is not treated as if it were 31.

For age and differences, the engine counts whole years first, then leftover months, then leftover days. It does not divide by 365, because no year is exactly 365 days once leap years enter the picture. For business-day counts it walks the date range day by day and drops Saturdays and Sundays. The result is the same number you would get by marking the dates on a paper calendar.

FAQ

Do my dates leave my browser?

No. Every calculation happens on your own device with JavaScript. The dates you enter are never uploaded to a server, and we do not set tracking cookies for the calculators themselves.

Are the results exact?

They follow the standard Gregorian calendar exactly, including leap years. They are intended for everyday and general use, not as official records for legal, payroll or government matters.

Which tool should I use?

Use the age calculator for birth dates, the date difference calculator for two arbitrary dates, add or subtract for shifting a date, business days for working-day counts, countdown for events, day of year / week number for calendar lookups, and birthday for your next birthday.

Reviewed by Daniel Okafor, senior editor