How this instrument works
This is a narrower, statutory cousin of household discretionary income. A budget's discretionary figure subtracts whatever you actually spend on rent and groceries from take-home pay. The federal formula behind income-driven repayment (IDR) subtracts a fixed proxy instead: 150% of the poverty guideline published for your household size and state, regardless of what your rent or grocery bill actually is. Two borrowers earning the same salary in different-sized households get different discretionary income here even if their real spending is identical, because the formula only ever looks at adjusted gross income (AGI) and headcount.
The 150% multiplier acts as an income shield — it exists so that a borrower earning near or below the poverty line for their household owes nothing at all, and the max(0, …) floor keeps that shield from ever producing a negative number. Once AGI clears the shield, the servicer takes 10% of what remains and divides by twelve for the monthly bill. That 10% rate belongs to the newer generation of plans — the SAVE plan, PAYE, and IBR for anyone whose first federal loan was disbursed on or after July 1, 2014; borrowers grandfathered into the original IBR plan owe 15% instead, a distinction this sheet assumes you already know applies to your loans.
Every field here resets once a year. Adjusted gross income comes from whichever tax return the servicer most recently pulled, so a raise or a job loss this month does not move the monthly payment until the next annual recertification. The poverty guideline itself is republished by the federal government every January and varies by household size and, for Alaska and Hawaii, by state — an outdated guideline entered here will quietly shift the discretionary figure even though nothing about the borrower's income changed.
- Enter last year's tax-return figure in the Adjusted gross income, $ field.
- Look up this year's guideline for your household size and enter it in Federal poverty guideline for household size, $.
- Read Annual discretionary income, $ — AGI minus 150% of that guideline, floored at zero.
- Read Monthly IDR payment, $ — the discretionary figure divided by twelve and charged at 10%.
- Raise the AGI field alone to see how much of a raise actually reaches the monthly bill once above the poverty floor.
Worked example — a $50,000 salary
A single borrower reports $50,000 of adjusted gross income against the 2024 one-person federal poverty guideline of $15,060. One and a half times that guideline is $22,590, and subtracting it from AGI leaves $27,410 — comfortably positive, so the floor never engages and the full amount counts as discretionary income for the year.
Dividing $27,410 by twelve gives a $2,284.17 discretionary base each month, and 10% of that base is $228.42 — the figure this sheet returns as the monthly IDR payment. A standard 10-year fixed schedule on a typical federal loan balance in that income range commonly runs several hundred dollars higher, which is the gap that makes income-driven repayment worth calculating rather than assuming.
Questions
What counts as adjusted gross income for this formula?
It is the AGI line from the federal tax return your loan servicer has on file, not your current salary or take-home pay. Because servicers pull this figure once a year at recertification, a recent raise, bonus, or job loss will not change the monthly payment shown here until the next annual update, even though your actual paycheck already has.
Why use 150% of the poverty guideline instead of my real expenses?
The federal formula is a fixed statutory shield, not a personal budget. A household discretionary-income calculation subtracts whatever you actually spend on rent, food, and utilities; this one subtracts a flat multiple of a published guideline tied only to household size and state. Two borrowers with identical rent can land on different payments here simply because their households are different sizes.
Why does the payment drop to zero below a certain income?
At $22,000 of AGI against the $15,060 guideline used here, 150% of the guideline is $22,590 — above the income itself — so discretionary income floors at zero and the monthly payment does too. That $0 bill is not a missed or delinquent payment; income-driven plans count qualifying $0 months toward the years required for eventual loan forgiveness.
Does every income-driven plan use a 10% rate?
No. This sheet's 10% matches the SAVE plan, PAYE, and the version of IBR available to borrowers whose first federal loan was disbursed on or after July 1, 2014. Borrowers grandfathered into the original IBR plan from before that date pay 15% of discretionary income instead, which produces a noticeably higher monthly figure from the same AGI.
Where do I find the poverty guideline for my household?
The federal government republishes it every January, broken out by household size, with separate and higher figures for Alaska and Hawaii. It is not something this sheet looks up automatically — entering last year's number after a household member is added, or after the annual update, will understate the guideline and overstate both the discretionary income and the monthly payment.
Why does the timing of loan repayment matter right now?
Federal student loan billing paused during the COVID-19 emergency and resumed in October 2023, pushing a large wave of borrowers to recertify income and re-enroll in an income-driven plan at once. Running current AGI and the current guideline through this formula shows what a resumed bill actually looks like, rather than relying on a pre-pause payment that no longer reflects either figure.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.