What discretionary income means here
Discretionary income in the student loan context is a term of art. It does not mean the money left after your rent and groceries — it means your adjusted gross income minus a multiple of the federal poverty guideline for your household size. Everything below that threshold is protected; a fixed percentage of everything above it becomes your annual payment.
Three numbers therefore determine your payment, and only three. The multiplier (how much income is protected — 100%, 150% or 225% of the guideline, depending on the plan), the percentage charged on the excess (5%, 10%, 15% or 20%), and the poverty guideline itself, which the Department of Health and Human Services publishes each January and which rises with household size and is higher in Alaska and Hawaii.
Your loan balance does not appear in that formula at all. This is the single most counter-intuitive feature of income-driven repayment and the source of most confusion: a borrower with $40,000 of debt and a borrower with $400,000 of debt, at the same income and household size, owe the same monthly payment. The balance only matters for two things — whether a plan's cap at the ten-year standard payment binds, and how much is left to be forgiven at the end.
The regulations governing these plans live at 34 CFR Part 685 for Direct Loans. They have been amended repeatedly, litigated, and revised by legislation, and specific plan names have come and gone. That is why every parameter on this page is editable: the arithmetic is stable even when the policy is not. Confirm the current multiplier, percentage and forgiveness period with your servicer or at the Department of Education's own site before acting on any figure here.
Working the formula, and the two things that override it
Start with the guideline. HHS publishes a one-person figure and a per-person increment; a household of four is the one-person figure plus three increments. Multiply by the plan's protection factor to get the protected amount, subtract it from AGI, and floor the result at zero — a borrower below the threshold has a calculated payment of $0, and on these plans a $0 payment still counts as a qualifying payment toward forgiveness.
Then apply the percentage and divide by twelve. That is the whole calculation.
Override one: the standard-payment cap. IBR and PAYE limit the payment to what you would pay on the ten-year standard plan. Once your income rises far enough that the formula exceeds that amount, the plan stops reducing anything, and you are simply on a standard plan with extra paperwork. The calculator applies the cap for those plans and tells you when it binds.
Override two: interest. The payment is set by income, not by what the loan needs. When the payment is smaller than the monthly interest, the shortfall is added to the balance and the debt grows — negative amortisation. This is not a malfunction; it is the intended consequence of decoupling the payment from the loan. Some plans have waived the uncovered interest so the balance holds flat instead. The checkbox on this page lets you model either treatment.
The forgiveness projection runs the loan forward month by month. Income and the poverty guideline are grown at the rate you enter, so your position relative to the threshold stays constant and the payment rises in proportion. Each year the payment is recomputed, each month interest accrues, and whatever balance survives to the forgiveness date is reported as the amount forgiven.
Worked example: $60,000 income, family of three, 10% plan
A borrower has an AGI of $60,000, a household of three, and $45,000 of Direct Loans at a 6% weighted average rate. The plan protects 150% of the poverty guideline and charges 10% of what is left.
- Poverty guideline. $15,650 for one person plus two increments of $5,500 gives $15,650 + $11,000 = $26,650.
- Protected income. 150% × $26,650 = $39,975.
- Discretionary income. $60,000 − $39,975 = $20,025.
- Annual amount due. 10% × $20,025 = $2,002.50.
- Monthly payment. $2,002.50 ÷ 12 = $166.88.
- Standard comparison. $45,000 at 6% over 120 months uses the factor 11.1021 per $1,000, so the standard payment is 11.1021 × 45 = $499.59. The formula is well below that, so no cap applies and the plan reduces the payment by $332.71 a month.
- Interest test. Monthly interest is $45,000 × 6% ÷ 12 = $225.00. The payment of $166.88 falls $58.12 short, so without an interest waiver the balance grows by $58.12 in the first month.
That last line is the one to sit with. The borrower is paying $166.88 a month and owing more each month. Over the first year, on a balance that is still near $45,000, the shortfall accumulates to roughly $700. The payment is affordable and the debt is growing at the same time — both statements are true, and the plan is working exactly as designed. What resolves it is either income growth pushing the payment above the interest, or forgiveness at the end of the term.
Raise the income to $100,000 with the same household and the discretionary figure becomes $60,025, giving a monthly payment of $500.21. That now exceeds the $499.59 standard payment, the cap binds, and the plan stops helping. Between $60,000 and roughly $100,000 of income, this borrower moves from deep negative amortisation to no benefit at all.
Reading your result
Compare the payment with the interest, not with the standard plan. A payment below the standard amount feels like a win, but if it is also below the monthly interest, the balance is rising. The interest gap output tells you which regime you are in, and it is the number that determines whether you are repaying a debt or holding it until forgiveness.
Decide which strategy you are running. There are only two coherent ones. Either you intend to repay the loan, in which case income-driven repayment is a temporary bridge and you should get off it as your income allows — the standard payment calculator shows what full repayment costs. Or you intend to reach forgiveness, in which case minimising the payment along the way is rational and the growing balance is irrelevant. Drifting between the two is the expensive option.
Take the forgiveness figure seriously as a tax question. Balances discharged under income-driven repayment have at various times been treated as taxable income to the borrower. A six-figure forgiveness event under a taxable regime produces a real tax bill in a single year. Check the rule in force for the year your forgiveness would occur, and if it is taxable, plan for it the way you would plan for any other lump-sum liability.
Recertify on time. Missing an annual income recertification typically moves you to a standard payment and can cause accrued interest to capitalise into principal, which permanently raises the interest you accrue thereafter. It is the most common and most avoidable way borrowers lose money on these plans.
Check whether refinancing makes sense — carefully. A private refinance can cut the rate, but it permanently forfeits access to income-driven repayment, forgiveness, and federal hardship provisions. The refinance savings calculator quantifies the interest saved so you can weigh it against what you would be giving up.
Protected income by household size and plan multiplier
| Family size | Poverty guideline | 100% (ICR) | 150% (IBR, PAYE) | 225% |
|---|---|---|---|---|
| 1 | $15,650 | $15,650 | $23,475 | $35,213 |
| 2 | $21,150 | $21,150 | $31,725 | $47,588 |
| 3 | $26,650 | $26,650 | $39,975 | $59,963 |
| 4 | $32,150 | $32,150 | $48,225 | $72,338 |
| 5 | $37,650 | $37,650 | $56,475 | $84,713 |
| 6 | $43,150 | $43,150 | $64,725 | $97,088 |
An AGI at or below the figure in your plan's column produces a $0 calculated payment. Alaska and Hawaii use higher guideline tables, so a borrower there has more income protected at every household size.
Plan parameters change — verify before you act
Federal income-driven repayment has been restructured several times, and individual plans have been created, closed to new enrolment, enjoined by courts and replaced by statute. The multipliers, percentages and forgiveness periods offered above reflect formulas that have been in use, but any of them may no longer apply to you. Treat this page as a way to understand and check the arithmetic, and take the parameters themselves from your servicer's disclosure or the Department of Education. The Custom plan option exists so the calculator still works when the published numbers move.
Assumptions and limits
- Only federal loans qualify. Private student loans have no income-driven option; the lender's contract is the whole of the deal.
- Filing status matters. Some plans count a spouse's income when you file jointly and exclude it when you file separately. Filing separately can lower the payment and raise the tax bill; model both before choosing.
- Parent PLUS loans are treated differently from student borrowing and generally reach income-driven terms only through consolidation, on less generous terms.
- Public service forgiveness runs on a payment count, not a clock. It requires 120 qualifying payments while employed full time by a qualifying employer, which need not be consecutive.
- The projection assumes steady income growth. Real recertifications reflect real income, which moves in steps and sometimes falls. Treat the year-by-year table as a scenario, not a forecast.
- Capitalisation events are not modelled. Leaving a plan, missing a recertification or consolidating can convert accrued interest into principal, which raises future accrual.
- Tax on forgiven balances is not modelled. The treatment has changed and depends on the year of discharge.
How income-driven repayment compares with the alternatives
The ten-year standard plan is the cheapest way to clear the debt if you can afford it, because every payment exceeds the interest from the first month. It is the benchmark this calculator reports alongside your income-driven figure, and the gap between the two is the monthly cash-flow relief you are buying.
Graduated and extended plans lower the early payments without reference to income. They stretch the term and raise total interest, but they avoid the annual recertification burden and they never produce a payment below the interest.
Private refinancing cuts the rate for borrowers with strong credit and stable income, and permanently ends eligibility for everything on this page. It suits someone with a high income relative to their balance who has no realistic path to forgiveness — the same borrower for whom the standard-payment cap already binds.
Aggressive prepayment is the right answer whenever the payment already exceeds the interest and forgiveness is out of reach. Use the loan payoff time calculator to see what an extra monthly amount does to the schedule.
One planning note that sits upstream of all of this: the size of the balance is decided years before the first payment. If you are still choosing how much to borrow, run the projection first with the college cost projection calculator, and keep an eye on how the resulting payment sits inside your future budget — lenders will, using the same ratio as the debt-to-income ratio calculator.