Effort and delivery date are different things
If a task is estimated at 40 hours, it is tempting to call it five days of work.
That is only true when one person can spend eight uninterrupted hours on the task on each of five consecutive working days. Most project calendars do not work that way.
Effort describes the amount of work. A delivery date says when that work can be completed in a real calendar.
Start with the amount of work
Begin with an estimate in hours or working days. It should cover the work that is actually needed, including relevant implementation, review, testing and delivery activities.
If the estimate is still uncertain, review scope, complexity and unknowns first. The Quick Task Estimate can help you produce a useful first planning value.
Use real daily capacity
Next, decide how many hours can genuinely be spent on this project each day.
This is not the length of the working day. Meetings, code review, client communication, production support and other responsibilities all reduce project capacity.
For a 40-hour estimate and six hours of daily capacity:
40 hours ÷ 6 hours per day = 6.67 working days
Plan for seven working days, not five. Read more about choosing capacity in How to Convert Estimated Hours Into Working Days.
Put those days into a real calendar
Seven working days do not necessarily equal seven calendar days. Weekends and public holidays can move the finish date even though the effort has not changed.
For international work, use the calendar of the person or team whose availability determines delivery. When several parties are involved, record external dependencies separately.
Add a buffer where it has a purpose
The date calculated directly from effort and capacity is a useful baseline. If the date will be communicated as a commitment, a modest buffer can cover normal variation such as small fixes, context switching or short communication delays.
A buffer should not hide major unknowns. If a critical integration has not been explored or the scope is still moving, clarify the work before adding another percentage.
The simplest model
Estimated effort
÷ real daily capacity
= required working days
Then:
Working days
+ work calendar
+ public holidays
+ a sensible buffer
= recommended delivery date
This remains an estimate, not a guarantee. It is still a much better planning basis than assuming that 40 hours always means five calendar days.
Use the Delivery Date Calculator to run the complete calculation.