The NSF, "as a general policy", will fund only up to two months' salary for senior personnel on its grants, which includes PIs and another category of, roughly, "people who smell like faculty." This rule doesn't apply for non-senior personnel. Also, while I haven't found this caveat on the NSF's website, I have seen on several university research offices' sites that the rule doesn't apply to "soft-money" people, i.e. those whose salaries are normally fully funded by grants.
I work at a private research institute (non-profit) whose income is entirely from grants, and thus we're all soft money here. I'm applying to an NSF grant as a PI and, while it seems like the two-ninths rule is probably binding on me as a PI at least in principle, it's not completely clear to me to what extent asking for more than two months' salary, say up to four or five, would be a big negative on our application. Does anybody have any experience with this? It's quite confusing especially because "under normal rebudgeting authority" it looks as if I would be fully within NSF rules to budget for salary for a colleague here but then rebudget to spend that money on my own salary after the award. Enclosing the relevant NSF policies below.
As a general policy, NSF limits the salary compensation requested in the proposal budget for senior personnel to no more than two months of their regular salary in any one year. (See Exhibit II-3 for the definitions of Senior Personnel.) It is the organization’s responsibility to define and consistently apply the term “year”, and to specify this definition in the budget justification. This limit includes salary compensation received from all NSF-funded grants. This effort must be documented in accordance with 2 CFR §200, Subpart E, including 2 CFR §200.430(i). If anticipated, any compensation for such personnel in excess of two months must be disclosed in the proposal budget, justified in the budget justification, and must be specifically approved by NSF in the award notice budget.[14]
Under normal rebudgeting authority, as described in Chapters VII and X, a recipient can internally approve an increase or decrease in person months devoted to the project after an award is made, even if doing so results in salary support for senior personnel exceeding the two-month salary policy. No prior approval from NSF is necessary unless the rebudgeting would cause the objectives or scope of the project to change. NSF prior approval is necessary if the objectives or scope of the project change.