Example 1 (simple): 40% done after 12 working days
- Pace = 40% ÷ 12 = 3.33% of the work per day
- Projected total = 12 ÷ 0.40 = 30 working days
- Remaining = 30 − 12 = 18 working days
These are the calculator's default inputs.
Estimated Time Remaining Calculator: How Long Is Left?
Enter how much work is done and how long it took to see the estimated time remaining, the projected total and the pace you need to hit a deadline.
Quick answer
Estimated time remaining = time elapsed ÷ share done − time elapsed. If 40% of the work took 12 days, the whole job takes 12 ÷ 0.40 = 30 days, so 18 days remain. This assumes you keep the same pace; add a deadline to see the pace you would need instead.
How to read your result
Say how far you are: a percentage, or units completed out of a total (pages, tickets, records, kilometres). Enter how long that took and choose the time unit. Optionally enter the time left until the deadline to compare your pace with the pace you need.
- Estimated time remaining: how much longer the work takes if your pace stays the same.
- Projected total time: elapsed plus remaining, which is the time the whole job takes at this pace.
- Current pace: the share of the job you finish per unit of time.
- Deadline check: on track when the remaining time fits in the time you have left.
- Pace needed and speed-up needed: the pace that finishes exactly at the deadline, and how many times faster that is than now.
The estimate is a straight-line projection. Work that speeds up or slows down, such as a first-draft phase followed by editing, needs a different method; for task-by-task ranges use the PERT calculator, and for earned-value based forecasts the schedule variance and SPI calculator.
Time remaining formulas
share done = percent ÷ 100, or units done ÷ total units
pace = share done ÷ time elapsed
projected total = time elapsed ÷ share done remaining = projected total − time elapsed
pace needed = (1 − share done) ÷ time left speed-up = pace needed ÷ pace
Everything is a ratio, so the unit cancels: the result is in whatever unit you used for the elapsed time. Use one unit for elapsed time and time left.
Worked examples
Each example uses numbers you can load into the calculator above; the results match the tool exactly.
Example 2 (realistic): 25 of 80 units in 10 days with 15 days left
A team has reviewed 25 of 80 contracts in 10 working days and has 15 working days until the deadline.
- Share done = 25 ÷ 80 = 0.3125; projected total = 10 ÷ 0.3125 = 32 days
- Remaining = 22 days, which is 7 days more than the 15 left, so the project is behind pace
- Pace needed = 0.6875 ÷ 15 = 4.58% of the work per day, against a current 3.13%: a 1.47x speed-up
When a straight-line estimate is wrong
The projection assumes the next unit of work takes as long as the average unit so far. That fails when the early work is the easy part, when a long tail of fixes follows the main build, or when the team size changes mid-way. Treat the result as a baseline, then adjust: if you expect the pace to fall by a quarter, lengthen the remaining time by a third.
For a bottom-up plan from tasks and hours use the task time estimator. To plan the whole project end to end use the project time calculator.
How to estimate time remaining by hand
- Write progress as a fraction. 40% is 0.40; 25 of 80 units is 0.3125.
- Divide elapsed time by that fraction to get the projected total: 12 ÷ 0.40 = 30.
- Subtract the time already spent. 30 − 12 = 18 remaining.
- To check a deadline, compare the remaining time with the time you have left.
- To find the pace you need, divide the work left (1 − 0.3125 = 0.6875) by the time left and compare it with the current pace.
Assumptions, limits and common mistakes
Assumptions and limits
- The pace is assumed to stay constant. Real projects speed up and slow down.
- Percent complete is only as accurate as the way you measure it. Units completed are usually more reliable than a gut feeling.
- Elapsed time and time left must use the same unit, and the unit should count only time the work was possible (working days rather than calendar days if weekends are off).
- The calculator does not project a calendar date; it works in the unit you choose.
Common mistakes
- Mixing units. Elapsed in working days and time left in calendar days gives a wrong comparison.
- Measuring percent complete by time spent. That turns the projection into a circular answer.
- Counting started work as done. Only finished units count.
- Ignoring a changing team. If people join or leave, the old pace no longer applies.
Frequently asked questions
How do I calculate estimated time remaining?
Divide the time elapsed by the share of work done, then subtract the time elapsed. If 40% of the work took 12 days, the total is 30 days and 18 days remain.
How do I calculate time left on a project?
Use the same method: work out the pace from progress so far, project the total, and subtract the time already spent. Add a deadline to compare the result with the time you have.
What pace do I need to hit a deadline?
Divide the work left by the time left. With 62.5% of the work left and 15 days to go you need 4.17% of the work per day. The tool also shows how many times faster that is than your current pace.
Can I use units instead of a percentage?
Yes. Choose "Units completed" and enter the units done and the total, for example 25 of 80 pages.
Why does the estimate change as I add more progress?
Each update gives the calculator a better measure of your real pace. Early estimates are rougher than estimates made after most of the work is done.
What units can I use?
Hours, working days, calendar days or weeks. Pick the one you measured elapsed time in, and use it for the time left as well.
Last updated 19 October 2026. Last reviewed 19 October 2026. Reviewed by Umesh Manral. Formulas and tests: methodology.