Lead-Time Date Estimator
Estimate a finish date from historical job durations and your work calendar. Compare nearest-rank percentiles, sample size and the observed range.
Starts with an editable example. Replace the dates and rules with your own.
Your calculation
Ready when you are
Choose your dates.
Select your counting rules and calculate.
Calculation details
| Step | Value |
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How to use this calculator
Enter the new start, working weekdays, closures and completed jobs with inclusive start/end dates. Choose a historical duration percentile.
The same work calendar counts both historical and future dates. Nearest rank selects observation ceil(percentile × sample size / 100) after sorting. A 50th-percentile result uses this rule even with an even sample size.
A worked example
Observed jobs of three, five and eight workdays give an 80th-percentile duration of eight days. Starting November 2, 2026 on a Monday–Friday calendar finishes November 11.
Is an 80th-percentile result an 80% delivery guarantee?
No. It is a summary of your historical sample. Changing work, small samples and different operating conditions can make future durations very different.
Which calendar and years are supported?
Use Gregorian dates from 1900 through 2100, with results in that range. Daily attendance, office, coverage and chore plans allow up to 366 dates; school cycles, course plans and milestones allow up to 731. Dependency and historical workday calculations scan at most 3,661 dates. Class-session searches allow 366 dates and 200 sessions. Time-zone tools use browser IANA rules and require a choice when local times repeat. Dates and policy rules are entered manually; no employer, retailer, school or local weather policy is inferred. Copy, CSV and printing include the calculation rules; calendar exports appear when the result contains dated events.
What happens to my dates?
Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.