NIH Activity Codes

An NIH activity code is the two-to-three-character alphanumeric code -- one or two letters followed by two digits, such as R01, K08, T32, F31, U01, or P01 -- that NIH assigns to classify a specific type of funding mechanism (grant, cooperative agreement, or fellowship) by the kind of support it provides, independent of the awarding Institute or Center, the scientific topic, or the specific Notice of Funding Opportunity (NOFO) issuing it. The activity code is the second element of a full NIH grant number (after the application-type digit and before the Institute/Center code and serial number), for example the 'R01' in '1 R01 CA123456-01.' A funding mechanism is correctly described as belonging to an activity code -- rather than being one -- when its scope, review criteria, budget structure, and duration are all defined NIH-wide (or Common-Fund-wide) by that code's own governing policy, rather than being invented ad hoc by a single NOFO.

ByCASRAI Editorial Board

· Last updated 23 Jul 2026

Worked examples

Is an instance

R01 (Research Project Grant), R21 (Exploratory/Developmental Research Grant), and R03 (Small Grant Program) are all R-series activity codes, but each carries its own budget cap, duration limit, and renewal rules set NIH-wide -- R21 and R03 have no Type 2 competing-renewal option, unlike R01.

Is an instance

K08 and K23 are both career-development activity codes with the same general structure (a mentored award supporting an individual's transition to independence), distinguished specifically by whether the recipient's research is patient-oriented (K23) or laboratory/non-patient-oriented (K08).

Looks similar, but isn't

Not an instance

A NOFO number such as PAR-23-206 is not an activity code -- it identifies one specific funding opportunity, which invites applications under a particular activity code (e.g. R34), but the same activity code is reused across many different NOFO numbers over time.

Not an instance

An Institute/Center designator such as CA (National Cancer Institute) or MH (National Institute of Mental Health) is not an activity code -- it identifies which NIH component is administering the award, not what kind of award it is.

An NIH activity code is the letter-and-number code — R01, K08, T32, F31, U01, P01, and dozens of others — that the National Institutes of Health uses to classify its funding mechanisms by type of support. It is not a topic area, not an Institute or Center, and not a single competition: the same activity code (R01, for example) is used across essentially every NIH Institute and Center, for almost any scientific topic within NIH’s mission, and across hundreds of individual Notices of Funding Opportunity (NOFOs) issued over many years. What the activity code fixes NIH-wide is the kind of award — its general purpose, review approach, typical budget and duration rules, and eligibility pattern.

Where the activity code sits in an NIH grant number

A full NIH grant number encodes several pieces of information in a fixed order, and the activity code is only one of them. Using 1 R01 CA123456-01 as an example:

Application-type digit (1) — whether the application is new (Type 1), a competing renewal (Type 2), a supplement (Type 3), or another administrative type.
Activity code (R01) — the funding-mechanism classification this term covers.
Institute/Center code (CA) — which NIH Institute or Center is administering the award (here, the National Cancer Institute).
Serial number (123456) — a unique number assigned to the specific application/project.
Suffix (-01) — the year of the current project period, sometimes followed by an amendment/resubmission letter such as A1.

Confusing the activity code with the Institute/Center code, the NOFO number (e.g. a PA, PAR, or RFA number), or the CFDA/Assistance Listing number is a common source of error for people new to reading NIH award documents — all of these are separate identifiers that can co-occur with the same activity code.

Major activity code series

NIH groups its dozens of activity codes into informal ‘series’ by leading letter. The major ones a research administrator will encounter most often:

R series — research grants. The largest and most varied series, covering everything from the standard investigator-initiated R01 (Research Project Grant) to the smaller, shorter R21 (Exploratory/Developmental Research Grant) and R03 (Small Grant Program). Not every R-series code shares R01’s rules — R21 and R03 both cap budget and duration well below R01 and, per NIH policy, do not carry a competing-renewal (Type 2) option.
K series — career development awards. Support a named individual’s transition to, or continuation of, research independence rather than funding a project on its own — for example the mentored K08 and K23 awards, distinguished by whether the recipient’s research is patient-oriented (K23) or not (K08). K-series awards typically require an approved mentoring or career-development plan.
T and F series — training and fellowships. T-series awards (institutional National Research Service Awards, e.g. T32) go to an institution, which then selects and supports a roster of trainees; F-series awards (individual NRSAs, e.g. the predoctoral F31 and postdoctoral F32) are held directly by the individual trainee who applied.
U series — cooperative agreements. Structurally similar to an R-series grant but with substantial NIH programmatic involvement built in — NIH staff participate in study design, work-plan approval, or steering-committee decisions, rather than acting as a hands-off funder. U01 is the cooperative-agreement counterpart to R01; other U-series codes (U19, UG3/UH3, and others) support multi-project or phased-milestone structures.
P series — program project and center grants. Fund a multi-project, multi-investigator program under a single award, typically built around a shared scientific theme and often including shared core resources — for example P01 (Research Program Project Grant).
DP-prefixed and other Common Fund codes. NIH’s Common Fund uses its own combined codes — for example DP1 (Pioneer Award) and DP2 (Director’s New Innovator Award) — for cross-cutting, trans-NIH initiatives that don’t sit under a single Institute or Center’s standard activity codes.

This list is illustrative, not exhaustive — NIH’s own activity-code index runs to well over 60 codes across these and other series (including, for instance, dedicated codes for SBIR/STTR small-business awards, which are themselves R-series codes: R43/R44/R41/R42).

Why the distinction matters for research administrators

Because review criteria, budget rules, allowable renewal types, and standard due dates are all set at the activity-code level (sometimes further refined by an individual NOFO), correctly identifying which activity code a given opportunity uses — before assuming it behaves like a more familiar one such as R01 — is a basic due-diligence step in reading any NIH funding opportunity. A NOFO that uses the R21 activity code, for instance, will not accept the kind of full-scale, multi-year budget appropriate to an R01 submission, regardless of how the science is framed, because R21’s $275,000/two-year ceiling is fixed by the activity code itself, not by that individual NOFO.

Worked example

A program officer’s email refers to ‘an R01-equivalent award.’ Read literally, this means the mechanism carries R01’s typical characteristics — investigator-initiated, full project-period budget flexibility, competing-renewal eligibility — even if its actual activity code differs (as with certain U01s that are administered R01-like apart from added NIH programmatic involvement). Treating ‘R01-equivalent’ as a genuine activity code, rather than shorthand describing R01-like characteristics, is the kind of category error this term is meant to prevent.

Counter-example

A funding opportunity’s PA, PAR, or RFA number (for example, PAR-23-206) is not an activity code — it identifies one specific Notice of Funding Opportunity, which may itself invite applications under one or several activity codes (an R34 NOFO, for instance, is issued and reissued repeatedly under different Institute-specific PAR numbers, but all of those NOFOs use the same R34 activity code). Similarly, an Institute/Center’s own two-letter code (CA for the National Cancer Institute, MH for the National Institute of Mental Health) classifies who is funding the work, not what kind of award it is, and is not an activity code.

Related terms

Use in your systems

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