🗓️ Date Add/Subtract Calculator
Add or subtract days, weeks, months, or years from a date.
About this tool
Takes a starting date and adds or subtracts a chosen number of days, weeks, months, or years, returning the resulting date along with its day of the week.
Handles calendar quirks like different month lengths and leap years automatically, since those are exactly the details that make this tedious to do by hand or with simple mental math.
Worked example
30 days after January 1 lands on January 31. Adding 1 month to January 31 lands on either February 28 or 29 (whichever the year has), since February doesn't have a 31st day.
How to use it
- Pick a starting date.
- Enter the amount of time to add or subtract.
- Choose the unit — days, weeks, months, or years.
- Choose Add or Subtract, then press Calculate new date.
Tips
- Adding "months" to a date near month-end can land on an unexpected day if the target month is shorter — the calculator follows standard JavaScript date rules, rolling over into the next month when needed.
- Useful for calculating deadlines, subscription renewal dates, or "90 days from today" style contract terms.
- For counting the number of days between two known dates instead of finding a new date, use the Date Difference Calculator.
FAQ
What happens if I add 1 month to January 31?
Since February doesn't have 31 days, the date rolls forward — the exact resulting day depends on standard calendar rollover rules, which can land you on a date in early March rather than the last day of February.
Does this account for leap years?
Yes — adding or subtracting years and months correctly accounts for February having 29 days in a leap year.
Can I subtract time instead of adding it?
Yes — use the Direction dropdown to switch between Add and Subtract.
From the blog: getting the most out of this tool
Contract deadlines, subscription renewals, and "remind me in 90 days" tasks are the everyday situations this tool is built for — the kind of date math that's simple in concept but easy to get subtly wrong once months of different lengths or a leap year get involved.
It's the natural companion to the Date Difference Calculator: that one answers "how far apart are these two dates," this one answers "what date do I land on if I move forward or back from here."
📖 Want the fuller explanation?
See Counting Business Days & Deadlines for the reasoning behind this calculation, with worked examples.