Quick answer
Working days = ceil(effort ÷ (people × hours per day)), counting Monday to Friday. 100 person-hours with 2 people at 6 productive hours a day takes 9 working days: starting Monday 3 March 2025, it finishes Thursday 13 March, 11 calendar days.
Enter total effort, people, hours per day and a start date. The calculator returns working days and the finish date. Use this project duration calculator to check your own figures.
Related tools: Focus Session (Pomodoro) Calculator: How many focus sessions and breaks fit in the time you have. Hourly Productivity Calculator: Output per hour, time per unit and the hours needed to reach a target. Pomodoro Sessions Calculator: Number of focus sessions that fit in the time you have.
How to use the Project Duration Calculator
- Enter total effort (person-hours) (0.01 or more).
- Enter people working on it (a whole number, between 1 and 1000). It starts at 1.
- Enter productive hours per person per working day (between 0.1 and 24). It starts at 6.
- Pick start date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Total effort (person-hours) | A number | ≥ 0.01 |
| People working on it | A whole number | ≥ 1, ≤ 1000, starts at 1 |
| Productive hours per person per working day | A number | ≥ 0.1, ≤ 24, starts at 6 |
| Start date | A calendar date | — |
Formula and method
Formula
working days = ceil(effort ÷ (people × hours per day)); finish = the working day (Monday to Friday) on which the last of those days falls
IEEE-754 double precision; shown to at most 6 decimal places.
Divides total effort by the team's daily capacity and rounds up to whole working days, then counts Monday-to-Friday working days from the start date (a weekend start begins the next Monday). Holidays, ramp-up, dependencies and part-time availability are not modelled; add contingency yourself. Adding people shortens the estimate only when the work can truly be shared.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Total effort (person-hours) = 100; People working on it = 2; Productive hours per person per working day = 6; Start date = 2025-03-03.
| Result | Value |
|---|---|
| Working days | 9 |
| Finish date | 2025-03-13 |
| Finish weekday | Thursday |
| Calendar days from start | 11 |
Example 2
Inputs: Total effort (person-hours) = 45; People working on it = 1; Productive hours per person per working day = 8; Start date = 2025-03-07.
| Result | Value |
|---|---|
| Working days | 6 |
| Finish date | 2025-03-14 |
| Finish weekday | Friday |
| Calendar days from start | 8 |
Example 3
Inputs: Total effort (person-hours) = 37.5; People working on it = 3; Productive hours per person per working day = 5.5; Start date = 2025-03-08.
| Result | Value |
|---|---|
| Working days | 3 |
| Finish date | 2025-03-12 |
| Finish weekday | Wednesday |
| Calendar days from start | 5 |
The first line is the headline result (working days). Below it the project Duration Calculator lists finish date, finish weekday and calendar days from start, which describe the same case from other angles. IEEE-754 double precision; shown to at most 6 decimal places.
Worked example
100 ÷ 12 = 8.33, rounded up to 9. Five days cover 3 to 7 March and four more 10 to 13 March.
Where this estimate stops applying
There is no holiday calendar, and effort is assumed divisible between people. Real projects add coordination overhead, so add a buffer.
How the result changes with total effort
Holding every other input at the first worked example, this table changes only total effort. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Total effort | Working days | Finish date | Finish weekday |
|---|---|---|---|
| 50 | 5 | 2025-03-07 | Friday |
| 100 | 9 | 2025-03-13 | Thursday |
| 200 | 17 | 2025-03-25 | Tuesday |
| 400 | 34 | 2025-04-17 | Thursday |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Total effort (person-hours): left empty shows "Enter total effort (person-hours)." beside that field and no result.
- Start date: left empty shows "Enter start date." beside that field and no result.
Choosing between the Project Duration Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Focus Session (Pomodoro) Calculator](/time/focus-time-calculator/) | time available, focus session and short break | Focus sessions |
| [Hourly Productivity Calculator](/time/hourly-productivity-calculator/) | units completed and hours worked | Units per hour |
| [Pomodoro Sessions Calculator](/time/pomodoro-sessions-calculator/) | time available, focus session and short break | Focus sessions |
| [Study Schedule Calculator](/time/study-schedule-calculator/) | first day of studying, exam date and total study hours needed | Hours per study day |
| [Time Allocation Calculator](/time/time-allocation-calculator/) | total time, activity 1 and activity 2 | Activity 1 |
Background: dates and times
Date and time results depend on the conventions a tool uses: whether the end date counts, whether weekends and holidays are skipped, how months of different lengths are handled and whether time zones are applied. This page states its convention, and the worked examples show it.
Dates use the Gregorian calendar and calendar days unless the page says otherwise; check deadlines against the rule in your contract or regulation.
Assumptions and limitations
- No holiday calendar
- Assumes effort is perfectly divisible between people
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for total effort (person-hours) and start date to confirm this.
Frequently asked questions
What if I add a third person?
With three people, 100 person-hours at 6 hours a day need 100 ÷ 18 = 5.6, rounded up to 6 working days.
Do weekends count?
No. Working days are Monday to Friday only, so a project that runs over a weekend finishes later on the calendar.
Why 6 productive hours?
Meetings and breaks reduce an 8-hour day.
What does the Project Duration Calculator calculate?
Working days and finish date for a project from total effort, team size and daily hours. It returns Working days, Finish date, Finish weekday and Calendar days from start.
What formula does the Project Duration Calculator use?
working days = ceil(effort ÷ (people × hours per day)); finish = the working day (Monday to Friday) on which the last of those days falls. Divides total effort by the team's daily capacity and rounds up to whole working days, then counts Monday-to-Friday working days from the start date (a weekend start begins the next Monday).
What do I need to enter in the project Duration Calculator?
You enter Total effort (person-hours), People working on it, Productive hours per person per working day and Start date.
How is the result rounded or limited?
IEEE-754 double precision; shown to at most 6 decimal places. No holiday calendar.
What are the limits of this calculator?
No holiday calendar. Assumes effort is perfectly divisible between people.
What is an example of a project Duration result?
With total effort (person-hours) 100, people working on it 2, productive hours per person per working day 6 and start date 2025-03-03, the working days is 9.
Where does the method come from?
The method follows: Capacity arithmetic; Monday to Friday work week.
Related calculators
- Focus Session (Pomodoro) Calculator — How many focus sessions and breaks fit in the time you have.
- Hourly Productivity Calculator — Output per hour, time per unit and the hours needed to reach a target.
- Pomodoro Sessions Calculator — Number of focus sessions that fit in the time you have.
- Study Schedule Calculator — Study hours per session needed to cover your total study time before an exam.
- Time Allocation Calculator — Split a block of time between activities by percentage.
- Time Blocking Calculator — Lay tasks back to back from a start time, with a buffer between blocks.
Sources
- Capacity arithmetic; Monday to Friday work week
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.