Where the formulas come from
Each plan's constants — percentages, brackets, poverty-guideline tables, terms — were transcribed from official publications, and every constant in the engine carries its source and retrieval date. The primary sources:
- RAP: Federal Student Aid's RAP information center, cross-confirmed by the Congressional Research Service summary of the statute.
- IBR, PAYE, ICR: the official IDR application's plan details and 34 CFR 685.209; ICR's 2026 income percentage factors from 91 FR 34815 (the June 2026 Federal Register update).
- Poverty guidelines: the 2025 and 2026 HHS tables from ASPE and the Federal Register, all three state groups, all family sizes.
- SAVE wind-down: the official SAVE court actions page.
The rules implementing RAP and Tiered Standard were published 2026-05-01 and are under active litigation. That's why a visible "Rules as of" stamp sits on every page: if a court or a new rule changes a value, the stamp tells you which version produced your numbers.
The formula for each plan
- RAP: annual payment = a bracket percentage (1–10%) of your entire AGI, ÷ 12, − $50 per tax dependent, floored at $10/month. Unpaid interest in an on-time month is waived; principal drops by at least $50/month via a matching credit; forgiveness after 360 payments. Brackets use "more than X, not more than Y" boundaries — exactly $100,000 is the 9% bracket. The full table is here.
- IBR: 10% (first loan on/after July 1, 2014) or 15% (earlier) of discretionary income — AGI minus 150% of the poverty guideline for your family size — ÷ 12, capped at the 10-year Standard amount, forgiveness after 20 or 25 years respectively.
- PAYE: 10% of the same discretionary income, capped at the 10-year Standard amount, forgiveness after 20 years; payments under $5 bill at $0 and $5–$10 bill at $10. Eligibility requires no federal balance as of Oct 1, 2007 and a Direct Loan disbursement on or after Oct 1, 2011. Retired no later than July 1, 2028.
- ICR: the lesser of (a) a 12-year amortization of your balance multiplied by an income percentage factor interpolated from the published table, or (b) 20% of AGI minus 100% of the poverty guideline. No Standard cap; forgiveness after 25 years counting only payments through July 1, 2028. Our implementation reproduces the Federal Register notice's own worked examples to the cent.
- Standard 10-year: level payments that amortize the balance. For borrowers already in repayment, official tools quote the current balance over the months remaining on the original schedule at the principal-weighted rate — so when you provide your servicer's scheduled payoff date, RepayCompass does the same; without it, a fresh 120-month amortization.
- Tiered Standard: level payments over 10/15/20/25 years by balance tier (<$25k / $25–49,999 / $50–99,999 / ≥$100k), $50 monthly minimum, only for borrowers with a loan or consolidation on or after July 1, 2026.
How projections work
Every plan is projected month by month over its full term: interest accrues monthly on principal, income-driven payments recompute annually using your income-growth assumption (default 4%/year, adjustable 0–8%), and the loop tracks balance, totals, and any forgiven amount. All money math runs in integer cents — rounding happens only at display time. Because incomes are grown, lifetime totals and dates here can differ from official quotes that assume flat income; first payments are directly comparable.
Estimated tax on forgiveness = projected forgiven amount × an assumed marginal rate (default 22%, adjustable), shown only when a plan projects forgiveness in 2026 or later. PSLF forgiveness is never taxed and is never given a tax estimate.
Which poverty guidelines are applied?
IBR, PAYE, and ICR subtract a multiple of the federal poverty guideline. Official tools were observed still applying the 2025 guidelines in July 2026, so RepayCompass defaults to 2025 to match what you'd be quoted — with a visible disclosure under the results and a switch to the 2026 table under Assumptions if you want the newer numbers.
How results are tested
The engine runs an automated suite (200 tests at this writing) including fixtures from a real borrower's official quotes: the StudentAid.gov IDR application's plan-by-plan payments and the Federal Register's ICR worked examples, reproduced within a dollar — most to the cent. Edge cases are tested explicitly: $0 income minimums, very high incomes hitting caps, family sizes past 8, balances that pay off before forgiveness, and the married-filing-separately rules. A property test asserts a RAP balance can never grow month-over-month with on-time payments.
Known conventions and limits
- One aggregate loan (for now). You enter a total balance and a weighted average rate. Official systems compute per loan, so an averaged rate can land a few cents a month off the official Standard quote; per-loan entry is planned.
- The RAP dependent credit is shown both ways, because the statute includes $50/month per dependent but official tools have been observed quoting without it — pending confirmation with servicers.
- ICR's factor table is held constant across projection years (the 2026 table is the last one published before the plan retires).
- Married borrowers with two federal-loan spouses: the pro-ration rules for RAP and PAYE aren't implemented yet — the tool says so rather than guessing.
- Parent PLUS isn't supported yet. Those loans follow different rules, so the tool stops rather than showing numbers computed under the wrong ones.
Spot a number that disagrees with an official quote? That's exactly the kind of report we want — send the details (never include your SSN or account numbers). For your actual options, your servicer and StudentAid.gov are the final word.