How to estimate event task durations
Every schedule rests on duration guesses, and most of the slips come from guesses nobody wrote down.
The short answer
Estimate each task twice: how many working hours it takes, and how many calendar days pass before it is finished. The gap between the two is waiting for approvals, replies and supplier turnaround.
Give every task a fast, likely and slow figure, note who gave it and on what basis, and treat the slow figure as the one that moves the date.
Effort and elapsed time are different numbers
A programme draft may need six hours of writing but ten days to finish, because the chair must review it and two speakers must reply. If you schedule the six hours, the date will be missed every time.
Record both. Effort tells you who is overloaded (see the committee workload planner). Elapsed time tells you where the task sits on the calendar.
Where a defensible estimate comes from
- The person who will do the work, asked for fast, likely and slow, not a single figure.
- Your own last event: how long did the same task really take, including the waiting?
- The supplier, in writing: ask for their stated turnaround and what they need from you before the clock starts.
- A second person who has done something similar, to challenge the estimate rather than replace it.
Use three figures, then pick one on purpose
Fast is what happens if nothing goes wrong. Slow is what happens if one thing goes wrong. Likely sits between them.
Use likely for ordinary tasks. Use slow for tasks with an outside party, a committee decision or a one-off item with no history. A task whose slow figure is much larger than its fast figure is a risk, so give it a named owner and an early check date.
What changes a duration or the sequence
- A committee that meets monthly turns a two-day review into a wait for the next meeting.
- Working-day rules: confirm which days your organisation and each supplier treat as non-working, rather than assuming a holiday calendar.
- Inputs that arrive late, such as speaker biographies, which hold up design and print.
- Tasks that cannot overlap because they need the same person.
- Rework loops: if a draft normally goes back twice, schedule three passes, not one.
Common mistakes
- Adding every task's slow figure together, which produces a schedule nobody believes. Use slow only where it matters, and see float and buffer planning.
- Copying a duration from another organiser's event without knowing what their team and approvals looked like.
- Leaving approval time out because it is not work. It is the most common source of slippage.
- Never revisiting estimates once the first tasks finish. Compare actual to estimate and correct the rest.
Worked example · Fictional example
A forum secretariat estimates its speaker pack
Fictional organisation and figures. Durations are hypothetical and shown only to illustrate the method.
A fictional professional-learning association is preparing a one-day forum. Its secretariat lists four tasks and asks the person doing each for fast, likely and slow figures in working days of elapsed time.
| Task | Effort (hours) | Fast | Likely | Slow | Basis |
|---|---|---|---|---|---|
| Draft speaker invitation pack | 5 | 2 | 3 | 5 | Last year's pack, secretariat officer |
| Chair review and approval | 1 | 1 | 3 | 7 | Chair travels; next council meeting is the fallback |
| Speakers return biographies | 1 per speaker | 5 | 10 | 20 | Last year: two speakers replied after a reminder |
| Design and proof programme page | 8 | 3 | 5 | 8 | Designer's stated turnaround, in writing |
Use this yourself
Task duration estimate table
Copy this into a spreadsheet, one row per task from your work breakdown. Fill the basis column honestly; a blank basis means the figure is a guess.
- Mark any task whose slow figure is more than double its fast figure as a risk and give it an owner.
- Add a final row for approval waits so they are visible.
- After the first three tasks finish, replace estimates with actuals and re-check the later rows.
| Task | Owner | Effort (hours) | Fast (days) | Likely (days) | Slow (days) | Basis or source | Waiting on |
|---|---|---|---|---|---|---|---|
Handle it in-house, or bring in help?
Your team can usually handle this when
- Your team has run this format before and kept records of how long things really took.
- Few tasks depend on outside parties or committee decisions.
- One person owns the schedule and can update it weekly.
Outside planning help earns its fee when
- This is your first event of this type and nobody can say what the slow figure should be.
- Several approvers or suppliers sit on the critical path and their turnaround is unknown.
- Past estimates have repeatedly been wrong and the committee no longer trusts the schedule.
Need durations your committee will trust?
An Event Blueprint can include a task list with durations, the basis for each figure, and the supplier and approval waits written into the timeline. A planner can also work through the slow cases with your team, so the dates you commit to are ones you can defend.
Questions organisers ask
How do I estimate a task I have never done?
Ask someone who has, and ask a supplier for a written turnaround. Use the slow figure for the schedule and mark the task as uncertain. Replace the estimate with the actual as soon as the task finishes.
Should I add a safety margin to every task?
No. Padding every task hides where the real risk is. Keep estimates honest and put a deliberate buffer where uncertainty is concentrated, using the approach in the float and buffer page.
Do public holidays need to be in the estimate?
Confirm the non-working days with your own organisation and each supplier instead of assuming them. Enter them as stated exceptions in the milestone back-planner so the calendar shows them.
Related resources
Content record: Draft. Written from the cited sources and checked by automated rules; not yet independently reviewed.