Date Calculator

How to use the date calculator

The tool has two modes: Add or Subtract shifts a date forward or back by an amount you specify, and Difference tells you how much time sits between two dates. Both handle leap years and variable month lengths correctly — something mental arithmetic quickly trips over.

Mode 1: Add or subtract time

1. Pick a starting date.
2. Choose whether you're adding or subtracting.
3. Enter the amount — days, weeks, months, or years. Adding one month to January 31 lands on the last day of February, because the tool clamps to the end of the target month rather than overflowing into March.
4. Read the resulting date. The weekday is shown alongside so you can see if that deadline lands on a Saturday.

Mode 2: Difference between two dates

1. Pick a start date and an end date.
2. Read the breakdown: full years, full months, remaining days, total days, total weeks, and the business-days-only count (Monday–Friday, excluding no holidays — add a few buffer days for public holidays in your region).

Use cases

Project deadlines, contract end dates, baby due-date windows, counting down to a trip, or verifying an employment start/end span for a visa or tax form. The business-days figure is the one HR and legal usually care about.