The test is comparative, not a feelings test. Under 26 CFR 53.4944-3(a)(2)(iii), in deciding whether a significant purpose is income or appreciation, "it shall be relevant whether investors solely engaged in the investment for profit would be likely to make the investment on the same terms as the private foundation." That is the practical question: would a commercial lender have written this loan at this rate to this borrower? If the answer is no, the concessionary element is evidence the purpose is charitable. The same subdivision adds the mirror-image protection: the fact that an investment turns out to produce significant income or capital appreciation is not, by itself, conclusive evidence of a disqualifying purpose. An investment that succeeds does not retroactively stop being program-related.
There is also a but-for test. Paragraph (a)(2)(i) treats an investment as made primarily for charitable purposes if it "significantly furthers the accomplishment of the private foundation's exempt activities and if the investment would not have been made but for such relationship between the investment and the accomplishment of the foundation's exempt activities." So the investment has to be traceable to the foundation's own program, not merely compatible with it.
The payout consequence is the reason foundations use the tool. Under 26 CFR 53.4942(a)-3(a)(2)(i), a qualifying distribution means "any amount (including program related investments, as defined in section 4944(c), and reasonable and necessary administrative expenses) paid to accomplish one or more purposes described in section 170(c)(1) or (2)(B)." A grant and a program-related investment therefore count the same way toward the annual distribution the foundation owes, even though the foundation expects the investment back and does not expect the grant back.
And the recycling is accounted for in the payout arithmetic itself. Because the outlay already earned distribution credit, the statute takes that credit back when the money returns. Section 4942(d)(1) defines the distributable amount as "the sum of the minimum investment return plus the amounts described in subsection (f)(2)(C)," and subsection (f)(2)(C)(i) is "amounts received or accrued as repayments of amounts which were taken into account as a qualifying distribution." A repayment therefore does more than fail to earn credit a second time: it increases what the foundation must distribute in the year the money is received, on top of the ordinary minimum investment return. Form 990-PF carries the adjustment on a line of its own, "Recoveries of amounts treated as qualifying distributions." One thing worth knowing if you go looking: the regulation at 26 CFR 53.4942(a)-2 has not caught up, because its own definition of the distributable amount predates the 1984 amendment that added the clause, so the regulation alone does not show the rule.
A program-related investment can stop being one, and there is a grace period. Paragraph (a)(3)(i) says the classification survives changes in form or terms made primarily for exempt purposes, and that a change made for the prudent protection of the investment does not ordinarily cost the status. But a "critical change in circumstances" can end it, and where that happens the foundation is not subject to the section 4944(a)(1) tax "before the 30th day after the date on which such foundation (or any of its managers) has actual knowledge of such critical change in circumstances."
What it is not. A mission-related investment is a market-rate investment chosen partly for its alignment with the foundation's mission. It is a perfectly ordinary portfolio decision, it is not excepted by section 4944(c), and it earns no payout credit. The two terms are a contrast rather than synonyms, and using them interchangeably is the commonest error in this vocabulary. Impact investing describes an investor's posture and can be market-rate or concessionary; a program-related investment is a defined tax category available only to a private foundation.