Person Months

Person months is the unit NIH requires for expressing how much effort a Program Director/Principal Investigator (PD/PI), faculty member, or other senior/key personnel devotes to a specific project. It is not a raw hour count and not simply a percentage on its own — it is a percentage of a person’s total professional effort converted into months, using the length of that person’s actual appointment as the multiplier. Because the conversion depends on appointment type, the same percentage of effort produces a different person-months figure depending on whether someone is paid on a calendar-year, academic-year, or summer-term appointment, which is the single most common source of confusion when people search for an ‘NIH person months calculator.’

The conversion formula

NIH’s own guidance states the calculation plainly: multiply the percentage of effort committed to the project by the number of months in the person’s appointment type. If the appointment itself is less than full time (for example, a 0.5 FTE position), that fractional FTE is multiplied in as well.

Person months = percent effort × months in appointment type (× FTE fraction, if the appointment itself is less than full time)

Appointment types: CY, AY, and SM

NIH recognizes three appointment bases, and an individual can hold more than one within a year:

• Calendar year (CY) — a 12-month appointment. This is the most straightforward case: the multiplier is always 12.
• Academic year (AY) — the length of the institution’s own defined academic year, most commonly 9 months, though some institutions define it as 9.5 or 10 months. Because the multiplier is smaller than 12, the same percentage of effort yields fewer person months than it would on a CY appointment.
• Summer term (SM) — the institution’s defined summer period, commonly 2 or 3 months, used when academic-year faculty are also paid for summer research effort outside their academic-year appointment.

Institutions set their own AY and SM lengths; NIH does not standardize them, which is why a person months figure is only meaningful alongside the appointment type it was calculated against.

Worked examples

• 20% effort on a 12-month CY appointment: 12 × 0.20 = 2.4 CY person months.
• 20% effort on a 9-month AY appointment: 9 × 0.20 = 1.8 AY person months — notably less than the CY figure above for the identical percentage of effort.
• NIH’s own published examples: 10% effort on a 12-month CY appointment = 1.2 CY person months (12 × 0.10); 35% effort on a 3-month summer term = 1.05 SM person months (3 × 0.35); 10% effort on a half-time (0.5 FTE), 12-month appointment = 0.6 CY person months (12 × 0.5 × 0.10).

Where the figure is used

Person months appear in three places across the NIH application and award lifecycle: the Senior/Key Person Profile of the proposed budget (at application), Other Support disclosures (which sum a person’s committed effort across all of their active projects, federal and non-federal, to check for over-commitment), and the annual Research Performance Progress Report (RPPR), where actual person months are reported against what was proposed. NIH’s own Person Months FAQ and interactive Percent Effort to Person Months conversion chart are the authoritative reference and calculation tool — most institution-built ‘person months calculators’ are simply a wrapper around this same formula and NIH’s published conversion chart.

Common mistakes

• Confusing person months with clock hours. Effort is a share of total professional activity for the institution, not a timesheet total — someone working long weeks does not thereby report more person months.
• Ignoring the appointment-type difference. The same percentage of committed effort converts to a different number on a 9-month AY appointment than on a 12-month CY appointment; using the wrong multiplier is a routine budget-preparation error.
• Treating proposed and actual person months as never needing reconciliation. NIH generally requires prior approval when a PD/PI’s committed level of effort drops by 25 percent or more from what was awarded, so a material gap between the proposed and actual figures reported in the RPPR is a compliance signal, not just a bookkeeping note.
• Letting an individual’s total person months across projects exceed their real appointment. Summing a person’s committed effort across every active NIH-supported (and other) project should not exceed the total months available in their appointment type in a given year — Other Support disclosures exist specifically to surface this kind of over-commitment.

How this relates to effort reporting generally

Person months is NIH’s specific unit for the same underlying concept covered more broadly in effort reporting methodologies: documenting that salary charged to, or effort committed to, a federal award reflects real professional activity. Person months is the number that goes on the NIH forms; the effort-reporting system (Plan Confirmation, After-the-Fact Activity Records, or Multiple Confirmation Records) is the institutional mechanism that generates and certifies the percentage behind that number. The percentage itself is calculated against a person’s institutional base salary, which is also the figure the NIH salary cap applies to when translating committed effort into a dollar request.