IBR starts by protecting a slice of your income. It takes your adjusted gross income (AGI), subtracts 150% of the federal poverty guideline for your family size, and charges a percentage of only what is left: 15% a year for most borrowers, or 10% if you are a “new borrower” — meaning you had no federal student loan balance before July 1, 2014. Divide that by 12 and you have the monthly payment.

Family size is generous here: it counts you, your spouse if you file jointly, your children, and anyone else who lives with you and gets more than half their support from you — none of them have to be tax dependents. A bigger family size means a bigger protected slice and a lower payment. If your AGI falls under the protected amount entirely, your payment is $0, and those $0 months still count toward forgiveness.

IBR has a ceiling RAP does not. Your IBR payment can never exceed what a 10-year standard plan would have charged on the balance you had when you entered the plan. However high your income climbs, the payment stops there — and since 2026, there is no income test to enroll, so high earners can use IBR precisely for that cap.

Whatever remains after 300 qualifying monthly payments — 25 years — is forgiven, or 240 payments (20 years) for new borrowers. What IBR does not do: waive interest. If your payment does not cover the month’s interest, the shortfall can build on your balance.

RAP works from your whole AGI, with no protected slice. Your income lands in a band that sets an annual base payment: $120 a year if your AGI is $10,000 or less, then 1% of AGI up to $20,000, 2% up to $30,000, and so on — one percentage point per $10,000 band — until income above $100,000 pays 10% of AGI. That annual amount is divided by 12, and $50 a month comes off for each dependent you claimed on your tax return. The floor is $10 a month; there is no $0 tier and, unlike IBR, no cap.

Only tax-return dependents count — usually your children. A spouse is never a RAP dependent, and neither is someone you support but do not claim. That is why this number is usually smaller than your IBR family size.

On-time payments earn two subsidies. Any interest your payment does not cover that month is waived — your balance does not grow. And if your payment cuts your principal by less than $50, the Department adds a matching principal payment toward a $50 monthly principal reduction. For borrowers whose payment is smaller than their monthly interest, this is RAP’s biggest advantage over IBR.

Whatever balance remains after 360 qualifying monthly payments — 30 years — is forgiven. That is five to ten years longer than IBR’s finish line.

You can move between IBR and RAP in either direction, at any time, with no exit payment. The trap is what happens to your forgiveness credit — because the two clocks do not share it equally.

The credit only flows one way. Months you paid under IBR (or other income-driven plans) count toward RAP’s 360-payment clock if you switch to RAP. But months you pay under RAP never count toward IBR’s 300- or 240-payment clock. Spend three years on RAP, switch back to IBR, and those 36 months bought you nothing toward IBR forgiveness — the regulation excludes them explicitly.

That asymmetry matters most for borrowers deep into an IDR clock. If you have 15 years of credit toward IBR’s 25-year forgiveness, RAP’s lower payment may be the expensive choice: your credit carries into RAP’s longer 30-year clock, but every month you sit there is a month that does nothing for the shorter IBR finish line you were close to.

Two things stay safe when you switch. PSLF credit: both plans qualify, so public-service borrowers keep earning their 120 payments on either. And your legacy-plan access — with one enormous exception: taking out any new federal loan, or consolidating, on or after July 1, 2026 permanently cuts off IBR and the other legacy plans. Do not borrow or consolidate your way out of the choice.

RAP tends to win for lower incomes with big balances. Its band percentages start at 1% of AGI, and its interest waiver stops the balance from growing when the payment runs small — the exact situation where IBR lets unpaid interest pile up.

IBR tends to win as income rises — and the cap is why. RAP charges its percentage on every dollar of AGI with no ceiling; IBR charges only the income above 150% of the poverty line and stops at the 10-year standard amount. A higher earner with a modest balance can pay hundreds more per month on RAP than on capped IBR.

IBR usually wins if you are close to forgiveness. Your banked IDR months finish an IBR clock in 20 or 25 years total; moving to RAP re-aims you at a 30-year finish line, and any RAP months are worthless to IBR if you come back.

Married borrowers get a lever. File separately and both plans use your income alone. Neither plan has a built-in marriage penalty — filing jointly when both spouses have loans prorates the payment by each spouse’s share of the combined balance rather than double-charging the household — but the filing-separately move is often IBR’s biggest advantage in one-earner or unequal-earner households.

Chasing PSLF? Pick the lower payment. Both plans qualify, the balance goes at 120 qualifying payments either way, and PSLF forgiveness is tax-free — so every dollar you avoid paying before then is a dollar you keep.

Primary sources: RISE final rule, 91 FR 23768 (effective July 1, 2026) — the payment formulas follow 34 CFR 685.209 as amended; the forgiveness-credit asymmetry follows 685.209(k)(4) and (k)(8); the PSLF treatment follows 685.219(b)(28). Poverty figures: 2026 HHS poverty guidelines.