inyourbrowser.com

Date calculator

Date calculator is a browser-based time tool with four modes: find days between two dates, add or subtract time from a date, calculate exact age, or count down to a future event. All calculations use your browser's native date support.

0 days between the two dates.
End date is same day
0 days
Weeks
0w 0d
Approx months
0.0
Approx years
0.00
Today: Jun 12, 2026

Calculation modes

Direct links for each date calculation type.

Days between dates
Calculate exactly how many days, weeks, months, and years are between two dates. Instant, in your browser.
Add or subtract days from a date
Find the date that is N days before or after any given date. Free in-browser date calculator.
Age calculator
Calculate your exact age in years, months, and days from your date of birth. Free, in-browser age calculator.
Days until a date
Count down to any future date. See exactly how many days and weeks remain. Free, in-browser countdown calculator.

How to calculate the difference between dates

  1. Enter the start date and end date using the date pickers.
  2. The tool calculates the difference in days, weeks, months, and years.
  3. Alternatively, enter a date and add or subtract a number of days to find a future or past date.
  4. All calculations happen instantly in your browser.

Common uses

  • Calculating how many days until an event or deadline
  • Working out someone's age or how long ago something happened, use Unix timestamp converter when dealing with epoch-based dates from APIs
  • Adding business days to a date for scheduling or contract deadlines. The percentage calculator helps when you need to express time elapsed as a fraction

Technical specification

  • Algorithm or formula: Difference mode subtracts two epoch millisecond values then converts to days, weeks, months, and years. Add or subtract mode mutates a Date with setDate, setMonth, or setFullYear. Business-day mode iterates day-by-day and skips Saturdays and Sundays.
  • Browser API or library: Native JavaScript Date. No external library.
  • Input limits: Any date the Date object accepts. Practical range covers any historical or near-future application.
  • Output: Difference in days, weeks, months, and years; new dates from add or subtract; weekday name; ISO date string.
  • Known limitations: Holidays are not detected (business days exclude only Saturdays and Sundays). Time-zone-sensitive calculations use the browser's local time zone.

Frequently asked questions

Is my data sent to a server?
No. All date calculations run entirely in your browser using JavaScript's built-in date functions.
Does the tool account for leap years?
Yes. The JavaScript Date API handles leap years correctly in all difference and addition calculations.
Can I calculate business days (excluding weekends)?
Yes. Enable the business days option to exclude Saturdays and Sundays from day-count calculations.
Can I add months or years to a date, not just days?
Yes. The add/subtract mode supports days, weeks, months, and years.

Reviewed and tested May 26, 2026.