Work backward from a deadline by subtracting days, weeks, or months from any date.
Resulting Date
Monday, August 31st, 2026
Last updated: August 2026
Calculate Past Dates Instantly
Reverse engineering a timeline can be frustrating when dealing with different month lengths. This tool allows you to instantly subtract any combination of days, weeks, months, or years from a specific date to find your exact starting point.
Common Ways to Use This Tool
Reverse project scheduling: subtract a task's duration from a hard deadline to find exactly when it must start.
Mailing and shipping lead times: subtract delivery time from an event date to find your latest "send by" date.
Compliance lookback periods: subtract a required window (like 90 days) from a reference date for audits or regulatory filings.
Historical record-keeping: find the exact date a fixed number of days before any known date.
Worked Example
Say a wedding is on September 20, and invitations need to arrive 3 weeks (21 days) beforehand. Subtracting 20 days from September 20 crosses back into the previous month and lands on August 31, leaving 1 more day to subtract → August 30. That's the latest mailing deadline to hit the 3-week buffer.
Perfect for Reverse Scheduling
If you have a hard deadline, the most efficient way to plan is to work backward. By subtracting the required duration of your tasks from the final due date, you can map out a perfect, error-free timeline.
Need to add days instead, or find the gap between two existing dates? Try our Add Days To Date tool or the general Date Calculator.
Frequently Asked Questions
Select your target date and enter the number of days you want to subtract. The calculator will instantly work backward to find the exact starting date.
This is incredibly useful for reverse-scheduling. If a project is due on Friday the 20th and takes 14 days to complete, subtracting 14 days tells you exactly when you must start.
Yes! The calculator perfectly accounts for leap years and varying month lengths as it counts backward through the calendar.
Enter the event date as your starting point, then subtract the number of days you need for delivery or processing time. For example, if invitations need to arrive 3 weeks before a wedding, subtract 21 days from the wedding date to find your mailing deadline.
Many regulatory and financial rules reference a fixed period before a specific date (for example, "the 90 days prior to termination"). Enter the reference date and subtract the required number of days to find the exact start of that lookback window.
Enter your final due date, then subtract the estimated duration of your last task to get its start date - which is also the due date for the task before it. Repeat for each task in your project to build a full backward schedule.
This page defaults to subtracting time from a date; the Add Days To Date tool defaults to adding time. Both use the same calculator underneath, so if you need to switch directions mid-calculation you can simply change the Action dropdown instead of leaving the page.
Not when the earlier month is shorter. For example, subtracting 1 month from March 31st lands on the last valid day of February (28th or 29th), not a nonexistent "February 31st" - the calculator handles this edge case automatically.
