Direct comparison
NIH Reference Letter vs Letter of Support
NIH Reference Letters (F/K awards, via eRA Commons) vs. Letters of Support: who writes each, how they're submitted, and why one person can't provide both.
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How do NIH Reference Letter, Letter of Support compare side by side?
The table below compares NIH Reference Letter, Letter of Support across 7 procurement-relevant dimensions, from what it evaluates through exclusion rule.
Side-by-side comparison
| Dimension | NIH Reference Letter | Letter of Support |
|---|---|---|
| What it evaluates | The applicant's/candidate's own qualifications and potential | The proposed project — a specific resource, role, or collaboration |
| Who writes it | A referee identified by the applicant (not the sponsor or co-sponsor) | A collaborator, core-facility director, consultant, or partner organization |
| NIH mechanisms that require it | F-series fellowships (F30/F31/F32/F33) and K-series career-development awards | No mechanism-specific requirement — used wherever a resource/collaboration commitment needs documenting |
| How many | Minimum 3, maximum 5 — fewer than 3 and the application is not reviewed | No NIH-mandated count |
| How it's submitted | Directly by the referee via eRA Commons — not through Grants.gov, not uploaded by the applicant | Compiled by the applicant as a PDF attachment inside the SF424 (R&R) application package |
| Confidentiality | Confidential — visible to reviewers, not the applicant | Not confidential — part of the visible application |
| Exclusion rule | Sponsor/co-sponsor barred; anyone providing a Letter of Support for the same application is barred from also being a referee | No equivalent NIH-wide exclusion, though conflicts affect credibility |
Common questions
Common questions about NIH Reference Letter vs Letter of Support
How many reference letters does an NIH F31 or K99 application need?
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A minimum of 3 and a maximum of 5. NIH will not review an application with fewer than 3 submitted reference letters.
Can the same person write both a reference letter and a letter of support for my application?
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No. NIH's fellowship guidance excludes anyone who is providing a Letter of Support for the application from also serving as a Reference Letter referee on that same application.
Do I upload my own reference letters?
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No. Reference letters are submitted directly and confidentially by the referee through the eRA Commons Reference Letter system. Letters of Support, by contrast, are compiled and uploaded by the applicant as part of the application package.
Can my sponsor write my reference letter?
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No. The applicant's sponsor and any co-sponsors are barred from serving as referees on fellowship and career-development applications.
Do R01 applications need reference letters?
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No. The Reference Letter requirement is specific to individual fellowship (F-series) and career-development (K-series) applications. R01 and most other research-grant mechanisms use Letters of Support instead, where relevant.
