What does a person-month represent?
A person-month summarizes human effort at a monthly scale. Six person-months mean roughly six full-time-equivalent months of work under the chosen planning convention.
It does not mean the project must last six months. The effort may be distributed across multiple people, but dependencies, role constraints and coordination determine the real schedule.
How many person-days and hours are in one person-month?
A common planning assumption is 20 working days per month and eight hours per working day. Under that convention, one person-month equals 20 person-days or 160 person-hours. Organizations using another working calendar should state their own standard explicitly.
| Example unit | Equivalent |
|---|---|
| 1 person-day | 8 person-hours |
| 1 person-month | 20 person-days |
| 1 person-month | 160 person-hours |
| 2 person-months | 40 person-days / 320 person-hours |
Why person-months are not project duration
Person-months measure effort while duration depends on sequencing, parallel work, critical-path activities, decision lead times and actual resource availability. Dividing twelve person-months by four people and calling the schedule three months is only a rough capacity calculation.
Person-month versus FTE
Person-month is often used to express work demand. FTE expresses available full-time-equivalent capacity over a period. A project may require six person-months while the team can provide only three FTE-months in the same window, revealing a capacity gap.
Skill distribution still matters: two half-time specialists may equal one FTE numerically, but they are not interchangeable if their roles are different.
Calendar time versus real project capacity
A person with 20 theoretical working days in a month may have only 12 days available for a project after operations, meetings, leave and other projects. Planning the person as a full person-month creates schedule risk before execution begins.
Using person-months in proposals and contracts
When person-month is a commercial unit, the contract should define the conversion standard and how part-time allocation, holidays and overtime are handled. Without this, two parties can use the same term but price and plan it differently.
- Working days per person-month
- Hours per working day
- Treatment of public holidays and leave
- Part-time and FTE conversion
- Overtime or weekend rules
- Relationship between effort unit, price and delivery schedule