Person-months: what they are and how to calculate them

The short answer

A person-month (PM) is one person's full working time for one month. To turn a share of someone's time into person-months, multiply the percentage of their effort on the project by the number of months of their appointment.

So one full-time person for a year is 12 person-months, someone spending half their time on a project for two years is also 12, and 0.5 PM in a single month means half of that person's month.

The formula, worked through

The US National Institutes of Health gives the clearest statement of the conversion, and its examples hold for any funder that counts effort in person-months:

The last row is the one people get wrong. Effort is a percentage of the person's appointment, not of a full-time year, so a part-time contract scales it down before the months are counted.

Over the life of a grant

Proposals usually ask for person-months over the whole project rather than per year, so multiply by the months the person is actually on the project, not by twelve:

• A postdoc at 100% for 36 months is 36 person-months
• A PI at 10% for 36 months is 3.6 person-months
• A research assistant at 50% for the last 18 months of a 36-month project is 9 person-months

One person's total across every grant they hold cannot exceed their capacity: 12 person-months a year on a full-time contract, and proportionally less on a part-time one. Each proposal can be right on its own and the person still be committed to 130 percent of their time once the grants overlap.

Academic, summer and calendar months

Person-months follow the person's appointment, so the same effort gives different figures on different contracts. NIH separates calendar-year, academic-year and summer-term months, and notes that institutions differ: some define the academic year as 9 months, others as 10.

Where a PI on a 9-month academic year spends 30% of it on a project, and 30% of a 3-month summer term, NIH asks for 2.7 academic months and 0.9 summer months, listed separately. If your staff are on twelve-month contracts, every person-month is a calendar month and the distinction does not arise.

Horizon Europe

The Horizon Europe application form asks for person-months in Part B, section 3.1. Each work package description gives the number of person-months for personnel, and table 3.1f, the summary of staff effort, gives the person-months over the whole duration of the planned work for each work package and each participant, with each work-package leader's figure in bold. The form asks that this section matches the costs in the budget table.

The form leaves the length of a person-month to you. FFG, Austria's national contact point for Horizon Europe, gives the usual definition: one person-month is the organisation's actual annual productive hours divided by 12, and those hours depend on national rules and internal working time models.

Person-months are a planning figure. When you report, Horizon Europe costs staff in day-equivalents against a daily rate, and the time records behind them are a separate question, covered in UniTimesheet's guide to Horizon Europe timesheets.

UKRI

UKRI budgets do not ask for person-months. The council budget forms ask for staff time as hours charged to the project, and STFC caps a project lead or co-lead at 1,650 hours a year, which it equates to 37.5 hours a week for 44 weeks. At that cap one person-month is 137.5 hours, so that is the conversion if you plan in person-months and apply to UKRI.

Two more rules from the same STFC guidance:

• Most project leads and co-leads are requested as directly allocated, because their time is an estimate. They can be directly incurred instead where an audit trail of their time on the grant can be provided.
• Salary costs requested for one person must not exceed 100% of full time equivalent across all grants.

Each council publishes its own budget guidance, so check the one you are applying to.

Common mistakes

• Counting effort as a share of a full-time year for someone on a part-time contract
• Multiplying by 12 when the person is only on the project for part of its duration
• Adding academic and summer months into one figure where the funder asks for them separately
• Person-months in the proposal that do not agree with the personnel costs in the budget
• One person committed to more than 12 person-months a year across all their grants, which nobody notices until the grants overlap

Where AllocBoard fits

Working this out once for a proposal is a spreadsheet job. Keeping it true for every person across every grant, month by month for the life of each one, is where spreadsheets give out, and it is what AllocBoard is built for:

• Allocations are recorded in person-months, per person, per project and per month, including partial allocations such as 0.5 PM
• Each person's allocations are summed across every project, and anyone over 100 percent in a month is highlighted
• Work packages carry person-month budgets, with effort distributed by equal split, proportionally or month by month
• Pre-award plans cost the bid with salary estimates and work packages, and carry over to the live project when the grant is awarded

Sources

This guide summarises each funder's own guidance. It is not financial or audit advice: your grant agreement, the call documents and your research office have the final word.

• NIH Extramural Nexus, What is a person month and how do I calculate it? (31 March 2017)

• European Commission, Horizon Europe application form, Part B (RIA and IA), version 5.1, 22 January 2026, section 3.1 and table 3.1f

• FFG, Personnel costs in the proposal in Horizon Europe

• UKRI, STFC guidance for applicants, project lead and project co-leads (updated 8 May 2026)