What is a “Person Month” & How Do I Calculate It?


A “person month” is the metric for expressing the effort (amount of time) principal investigators (PIs), faculty and other senior personnel devote to a specific project. The effort is based on the type of appointment of the individual with the organization; e.g., calendar year (CY), academic year (AY), and/or summer term (SM); and the organization’s definition of such. For instance, some institutions define the academic year as a 9-month appointment while others define it as a 10-month appointment.

Conversion of percentage of effort to person months is straight-forward. To calculate person months, multiply the percentage of your effort associated with the project times the number of months of your appointment. For example:

25% of a 9 month academic year appointment equals 2.25 (AY) person months (9 x 0.25= 2.25)

10% of a 12 month calendar appointment equals 1.2 (CY) person months (12 x 0.10 = 1.2)

35% of a 3 month summer term appointment equals 1.05 (SM) person months (3 x 0.35= 1.05)

10% of a 0.5 FTE 12 month appointment equals 0.6 (CY) person months (12 x .5 X .1 = 0.6)
Another example:

If the regular pay schedule of an institution is a 9 month academic year and the PI will devote 9 months at 30% time/effort and 3 months summer term at 30% time/effort to the project, then 2.7 academic months and .9 summer months should be listed in the academic and summer term blocks of the application (9 x 30% = 2.7 person months; 3 x 30%= .9)

An Excel-based Percent of Time & Effort to Person Months Calculator is available on grants.nih.gov.

Have additional questions related to NIH’s usage of “person months”? Visit our page of frequently asked questions (FAQs) on this topic.



    1. Since it’s a 12-month Contract you will just use the 12 months calendar formulae,
      You will use the Calendar Year (CY) where you divide your annual salary with 12 ie
      1/12 * x= Y (Your monthly salary will Y), then depending on the % of effort you use,
      multiply with the CY i.e (%* CY) then you will get CY Months, then Multiply your
      Your monthly salary and the CY months to get the budget figure for that effort.
      i.e (Y*CY Months)

  1. How would a CM be listed for a person who is .5 FTE and put 50% of that FTE on a grant/contract? Our department has 12 month faculty.

  2. What is the % effort for someone working 0.5 summer months? What is the formula to calculate % effort during the 3 summer months? I can’t get it right! Is it 4.5% effort? Please help. Thanks, June

  3. Does person month also imply salary is drawn from that project? e.g. A researcher puts in one day per month (0.05 person months, calendar year) for consultation on a project but does not draw a salary/compensation from the project. Would this still be put as 0.05?

    1. The person months presented should represent the total effort on the grant regardless of compensation.

  4. Hello
    How can I divide the salary between my partners in our project based on person-month?
    thank you for your help

  5. How do you calculate hourly staff (i.e. undergrad students/temporary)? If they are committed 100% effort per month but work a varying schedule, sometimes a couple hours only, how do you calculate that?

  6. How does the formula compensate for effort that occurred only during a fraction of the year’s compensation for an employee? for example a postdoc who contributed to the project 25% effort 3 months of a 12 month calendar appointment? I think that would be 6.25% effort in a 12 calendar month = 0.0625X12=0.75 calendar months

Before submitting your comment, please review our blog comment policies.

Leave a Reply

Your email address will not be published. Required fields are marked *