Task Time Estimator: Estimate Project Time From Tasks and Hours
List your tasks and their hours, describe the team, and get the duration, finish date, hours per person and a breakdown by role.
Quick answer
Add up the hours of every task, add a buffer for the unknown, then divide by what the team can do in a day. 176 hours plus a 10% buffer is 193.6 hours; three people working 7 hours at 80% availability do 16.8 hours a day, so the work takes 12 working days.
How to read your result
List each task with the hours you expect it to take and, if you want a split by role, who does it. Then describe the team and the schedule: the buffer, the number of people, productive hours per day, availability and working days per week. A start date turns the duration into a finish date.
Duration: planned hours divided by the team's hours per day, rounded up to whole working days.
Finish date: that many working days counted from the start date, skipping weekends.
Total effort and the buffered effort: what the task rows add up to and what the plan actually reserves.
Hours per person and person-days: how the planned hours spread across the team.
Cost: planned hours times the hourly rate, shown only if you enter a rate.
Two tables sit below the numbers: hours by role (with each role's share) and three team-size scenarios, so you can see what a smaller or larger team does to the date. The calculator is a bottom-up estimate, where every task is estimated separately. For ranges of uncertainty per task use the PERT calculator.
Bottom-up estimate formulas
planned hours = Σ task hours × (1 + buffer ÷ 100)
team hours per day = people × hours per day × availability ÷ 100
working days = ⌈ planned hours ÷ team hours per day ⌉
hours per person = planned hours ÷ people person-days = planned hours ÷ hours per day
Cost is planned hours times the hourly rate. The scenario table repeats the working-days formula with half the team (rounded up, at least one person) and twice the team.
Worked examples
Each example uses numbers you can load into the calculator above; the results match the tool exactly.
Example 1 (simple): a five-task website build
Design 24 h, frontend 60 h, backend 48 h, QA 32 h and documentation 12 h, with a 10% buffer, three people at 7 hours a day and 80% availability, and a rate of 55 an hour.
Total effort = 24 + 60 + 48 + 32 + 12 = 176 hours; with the buffer = 193.6 hours
Team capacity = 3 × 7 × 0.8 = 16.8 hours a day; 193.6 ÷ 16.8 = 11.52, rounded up to 12 working days
Starting Monday 2 November 2026 the work finishes Tue 17 Nov 2026
Hours per person = 64.53; person-days = 27.66; cost = 10,648
The role table shows the two developers carry 108 of the 176 hours (61.4%). The scenario table shows 2 people need 18 days and 6 people need 6.
Example 2 (realistic): one person, no buffer, unassigned work
A freelancer plans three tasks: setup 10 h, build 14 h and docs 16 h, with no role entered for the first two and "Dev" for docs, working alone at 8 hours a day and 100% availability.
Total effort = 40 hours (no buffer)
Capacity = 1 × 8 × 1.0 = 8 hours a day; 40 ÷ 8 = 5 working days, finishing Fri 6 Nov 2026 from a Monday 2 November start
Bottom-up estimates add up the parts, so any missing task is missing from the total. The usual causes are forgotten work (review, rework, deployment, meetings), optimism in the individual numbers, and capacity assumptions that ignore holidays and interruptions. The buffer field is the simplest defence: 10% is a floor for familiar work and 25% to 50% is common for new technology.
To estimate the uncertainty rather than hide it in a buffer, put optimistic, most likely and pessimistic values for each task into the PERT calculator, or run them through the project duration simulator. For tasks that depend on each other, use the critical path calculator; this estimator assumes capacity is the only constraint.
How to estimate project time bottom-up by hand
Break the work into tasks small enough to estimate in hours.
Estimate each task and add them: 24 + 60 + 48 + 32 + 12 = 176 hours.
Add a buffer. 176 × 1.10 = 193.6 hours.
Work out team hours per day. 3 people × 7 hours × 80% = 16.8.
Divide and round up. 193.6 ÷ 16.8 = 11.52, so 12 working days. Count 12 working days from the start date to get the finish date.
Assumptions, limits and common mistakes
Assumptions and limits
Capacity is the only constraint. Dependencies between tasks, handoffs and part-time overlap are not modelled.
Everyone is assumed to work the same hours per day at the same availability.
Holidays are not removed from the finish date. Use the project time calculator to enter a holiday list.
The scenario table scales the same effort with team size. In real projects adding people also adds communication overhead.
Common mistakes
Using 8 hours a day. Most people spend less than a full day on project work.
Skipping the buffer. Unknown work always arrives; leaving 0% assumes it will not.
Doubling the team to halve the time. Handoffs and onboarding mean the real gain is smaller.
Mixing person-days and elapsed days. 27.66 person-days is not 27.66 calendar days.
Frequently asked questions
How do I estimate time for a project?
List the tasks, estimate each in hours, add them, add a buffer, and divide by the team's daily capacity. This is the bottom-up method this calculator uses.
What is a good buffer percentage?
10% is a floor for familiar work. New technology, unclear scope or external dependencies often warrant 25% to 50%. Choose the buffer from your own history if you have it.
How many people do I need to finish by a date?
Divide the planned hours by the working days available times hours per day times availability. The project time calculator has a mode that solves for team size.
What is the difference between hours and person-days?
A person-day is the amount of work one person does in one working day, so planned hours divided by hours per day. It measures effort, not elapsed time.
How is the finish date calculated?
The calculator counts the working days from the start date, counting the start date as day 1 and skipping weekends. Holidays are not removed.
Can I export the estimate?
Yes. "Download CSV" saves the tasks, inputs, results and hours by role. "Copy result" copies the summary and a link that reproduces your inputs.