Add or subtract from a date
Start from any date and add or subtract days, weeks, months, or years to find the resulting date.
How date addition and subtraction work
The calculator applies each unit in order: years first, then months, then weeks and days. This matters for month arithmetic — adding 1 month to January 31st gives February 28th (or 29th in a leap year), not March 3rd.
Weeks and days are combined and added as a flat number of days. Hours and minutes are not adjusted — the result is always midnight on the calculated date in your local time zone.
Common uses
- 30/60/90-day deadlines — "what date is 30 business days from today?"
- Subscription and contract dates — when does a 12-month contract expire?
- Return windows — what's the last day to return an item bought on a given date?
- Project milestones — count forward from a kickoff date to map out phases
- Age milestones — when will someone turn exactly 10,000 days old?
Looking backward: what was the date N days ago?
Use the Subtract mode to go back in time. For example, subtract 90 days from today to find what date it was 90 days ago. For a dedicated "what was the date in the past?" tool, see what was the date.
Start noticing what matters.
Download Left on your iPhone to see the time you have left, dates you are looking forward to, build the habits you want to keep, and become a better version of yourself.
Scan with your camera to find Left on the App Store. Or search "Left" on the App Store.