Add / Subtract Days — Free Online Tool
Add or subtract days, weeks, or months from any start date.
About Add or Subtract Days
The Add or Subtract Days calculator lets you take any start date and move forward or backward by a set number of days, weeks, or months to find the exact resulting date. It is perfect for working out deadlines, due dates, project milestones, warranty expirations, or any event that falls a fixed interval from a known day.
Everything runs instantly in your browser, so there is nothing to install and no data is sent to a server. Just pick a date, choose to add or subtract, enter the amount, and the tool shows the full weekday-aware result along with its ISO format for easy copying into spreadsheets or other apps.
How to Use Add or Subtract Days
- Select your start date using the date picker.
- Choose whether to add or subtract from the operation menu.
- Enter the amount and pick the unit: days, weeks, or months.
- Click Calculate to see the resulting date, then use Copy to save it.
Key Features
Add or subtract days, weeks, or months from any date
Handles month-length and leap-year differences automatically
Shows the full weekday name plus a copy-ready ISO date
Instant results with no page reload
100% client-side processing for complete privacy
Works on desktop, tablet, and mobile browsers
Frequently Asked Questions
How does adding months handle different month lengths?
When you add or subtract months, the tool shifts the calendar month and keeps the same day where possible. If the target month is shorter, the date rolls to the nearest valid day, just like a normal calendar would.
Can I subtract days to find a past date?
Yes. Choose the Subtract operation and enter the number of days, weeks, or months you want to go back, and the tool returns the earlier date.
Does the calculator account for leap years?
Yes. Date math is based on the real calendar, so February 29 in leap years and varying month lengths are all handled correctly.
What is the ISO date shown in the result?
The ISO line displays the result in YYYY-MM-DD format, which is ideal for spreadsheets, databases, and other tools that expect a standard date format.