Pick a deadline, enter the work days you need and some buffer days, and get the date to start. Skip weekends if you want, and see milestones along the way.
Holidays are not skipped. Add one buffer day for each holiday in the period.
How the start date is worked out
Planning backward starts from the date you cannot move. The tool takes your deadline, adds the work days you need to the buffer days you want to keep in reserve, and counts that many days back to find the date to start.
You can count every calendar day or only weekdays. It also shows three milestones between the start and the deadline: the 25% mark, the halfway point, and the start of a final review. They give you dates to check your progress against.
Deadlines worth planning backward from
Papers, reports, and assignments
Work back from the due date to see when research has to be done and writing has to begin, and add buffer days for revisions.
Client work and project delivery
Count back from the delivery date with weekends skipped, and use buffer days for review rounds and changes.
Events and campaigns
Find the date to start from the day of the event, then use the milestones to check that bookings and announcements are on track.
Applications and paperwork
For forms with a submission deadline, count back to when to start gathering documents, with weekends skipped for offices that are closed.
How to find your start date in 4 steps
- Pick the deadline in the Deadline (due date) field.
- Enter the Work days you need and the Buffer days you want to keep in reserve.
- Turn on Skip weekends if only weekdays count as working time.
- Read the Recommended start date and the milestones below it.
Note: The result updates as you change any field, and there is no calculate button.
What the calculation counts
- The deadline day is not counted: the count starts on the day before the deadline, so the work and the buffer end the day before it.
- Total time: work days plus buffer days. The milestones are placed as a share of this total, not of the work days alone.
- Weekends and holidays: Skip weekends removes Saturdays and Sundays. Holidays are not skipped, so add a buffer day for each one.
- Whole days only: the tool does not work in hours. Entries are rounded down to whole days, and each field accepts up to 3,650 days.
- Short schedules: with only a few days in total, two milestones can fall on the same date.
Examples: deadline, days, and start date
Sample results for the same inputs you can enter above. Weekends counted means every calendar day is counted.
| Deadline | Work days | Buffer days | Weekends | Start date |
|---|---|---|---|---|
| Fri, Nov 20, 2026 | 5 | 0 | Counted | Sun, Nov 15, 2026 |
| Fri, Nov 20, 2026 | 5 | 0 | Skipped | Fri, Nov 13, 2026 |
| Fri, Nov 20, 2026 | 10 | 2 | Skipped | Wed, Nov 4, 2026 |
| Fri, Dec 18, 2026 | 14 | 0 | Counted | Fri, Dec 4, 2026 |
| Mon, Nov 30, 2026 | 3 | 0 | Skipped | Wed, Nov 25, 2026 |
| Mon, Nov 30, 2026 | 3 | 1 | Skipped | Tue, Nov 24, 2026 |
A holiday inside the period
Thanksgiving is Thursday, November 26, 2026. The fifth row above counts it as a working day. The sixth row adds one buffer day for it, which moves the start date one weekday earlier.
The same calculation in Excel
Excel's WORKDAY function takes a negative number of days to count backward and an optional list of holidays to skip. This tool gives you the same weekday count without a spreadsheet, and adds the buffer and the milestones.
Calendar days, working days, and buffer
Three choices decide how early you need to start. Here is how each one changes the result.
Calendar days or working days
If the work can happen on any day, count calendar days. If it happens only on weekdays, as with most office and client work, turn on Skip weekends.
The same deadline and the same number of days can give very different start dates. In the examples above, 5 days before Friday, November 20 is November 15 with weekends counted and November 13 with weekends skipped.
Why the deadline day is not a work day
The tool treats the deadline as the moment the work is due, so the last day of work is the day before. This keeps you from planning to finish on the day it is due.
If you do plan to work on the deadline day itself, reduce the work days by one.
Using buffer days
Buffer days are time you set aside on purpose for reviews, changes, and delays. They are added to the work days before the tool counts back, so a longer buffer moves the start date earlier.
Use them for holidays too, since the tool does not skip those. There is no fixed number that fits every project, so base it on how much could go wrong.
Common mistakes when counting back from a due date
Forgetting holidays and days off
The count looks right on weekdays, but a holiday or a company day off falls inside the period, so you have one less working day than you planned for.
💡 See the solution▼
Counting the deadline day as a work day
You plan to finish on the due date itself, so any delay on that day means you miss it.
💡 See the solution▼
Leaving out time for review and changes
The plan has exactly the number of days the work takes, so one revision or one delay pushes you past the deadline.
💡 See the solution▼
Not saving the dates
You work out the start date and the milestones, then forget them a day later.
💡 See the solution▼
Deadline calculator FAQ
Q.How is the start date calculated?
A. The tool adds your work days and buffer days to get the total, then counts that many days back from the deadline. The deadline day itself is not counted, so the work ends the day before the deadline. For example, with a deadline of Friday, November 20, 2026, 5 work days, and no buffer, the start date is Sunday, November 15, or Friday, November 13 if you skip weekends.
Q.What does Skip weekends do?
A. With it on, Saturdays and Sundays are not counted, so the total is counted in weekdays and the start date is always a weekday. The milestone dates are counted the same way. With it off, every calendar day counts. If you leave out holidays and use only weekdays, the result matches Excel's WORKDAY function with a negative number of days.
Q.Does it skip holidays?
A. No. Only weekends can be skipped. Holidays are not in the calculation, because they differ by country, state, and employer. Add one buffer day for each holiday that falls in the period. For example, if Thanksgiving, which is Thursday, November 26, 2026, falls inside your schedule, add one buffer day.
Q.What are the milestones?
A. They are three checkpoints placed as a share of the total time, which is work days plus buffer days: the 25% mark, the halfway point, and the start of a final review in the last 10% of the time. When Skip weekends is on, they fall on weekdays. For a short schedule, two milestones can land on the same date, because the tool works in whole days.
Q.What if the start date has already passed?
A. The start date turns red and a notice says it has passed. That means the work and buffer you entered no longer fit before the deadline. Shorten the work days or the buffer, or ask whether the deadline can move. If the deadline itself is in the past, the notice says so.
Q.Can I add the dates to my calendar?
A. Not directly. The tool shows the start date and the milestone dates, and you can enter them in your calendar or task app yourself. It does not connect to any calendar.
Q.Are the dates affected by my time zone?
A. No. The tool uses the calendar date you pick and counts days on your device's calendar, so the date you choose is the date it counts from. It works in whole days, not hours. Work days and buffer days are rounded down to whole numbers and can be up to 3,650 each.
Q.Is my data sent to a server?
A. No. The dates and numbers you enter are used only in your browser, and the page has no upload step. Closing or reloading the page clears them.
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