How to Calculate Income-Driven Repayment Payments on Student Loans

The Payment Formula Is Simple. The Plan Selection Is Not.

Income-driven repayment payments follow a consistent structure. The federal government defines your discretionary income, applies a plan-specific percentage, and divides by 12. That is the entire calculation.

The complexity sits in three variables: which poverty guideline applies to your household, which plan you qualify for, and how your income changes over time. Get any of those wrong and you will pay more than necessary, sometimes far more.

This guide shows you the exact math for each major plan, with worked dollar examples at two income levels.

Step 1: Calculate Your Discretionary Income

Every IDR plan starts here. Discretionary income is your adjusted gross income minus a percentage of the federal poverty guideline for your household size and state of residence.

The percentage varies by plan:

• SAVE (Saving on a Valuable Education): 225% of the poverty guideline
• PAYE and IBR (new borrowers): 150% of the poverty guideline
• IBR (older borrowers, pre-July 2014): 150% of the poverty guideline
• ICR (Income-Contingent Repayment): 100% of the poverty guideline

For 2025, the federal poverty guideline for a single person in the contiguous 48 states is $15,060.

SAVE discretionary income formula: AGI minus (2.25 x $15,060) = AGI minus $33,885

PAYE/IBR discretionary income formula: AGI minus (1.50 x $15,060) = AGI minus $22,590

The higher the protection threshold, the less of your income counts as discretionary. SAVE protects the most income. ICR protects the least.

Step 2: Apply the Plan-Specific Percentage

Once you have your discretionary income, the monthly payment calculation is straightforward.

Monthly payment equals: (Discretionary income x plan rate) divided by 12.

Worked Example 1: Single Borrower, $52,000 AGI, Undergraduate Loans Only

This borrower has $38,000 in federal undergraduate loans at 5.5% interest. They have no dependents and live in a contiguous state.

SAVE calculation:

• Discretionary income: $52,000 minus $33,885 equals $18,115
• Annual payment at 5%: $18,115 x 0.05 equals $905.75
• Monthly payment: $905.75 divided by 12 equals $75.48

PAYE calculation:

• Discretionary income: $52,000 minus $22,590 equals $29,410
• Annual payment at 10%: $29,410 x 0.10 equals $2,941
• Monthly payment: $2,941 divided by 12 equals $245.08

IBR (new borrower) calculation:

• Same discretionary income as PAYE: $29,410
• Same rate: 10%
• Monthly payment: $245.08

The gap between SAVE and PAYE here is $169.60 per month. Over 12 months, that is $2,035.20. Over five years, $10,176.

This borrower qualifies for SAVE and earns less than the standard 10-year repayment amount. SAVE is the clear choice at this income level.

Worked Example 2: Married Borrower, $94,000 Household AGI, Mixed Loan Types

This borrower has $67,000 in federal loans: $42,000 undergraduate, $25,000 graduate. They have one dependent child. Household size is three.

For a household of three in 2025, the federal poverty guideline is $21,150.

SAVE calculation:

• Protection threshold: 2.25 x $21,150 equals $47,587.50
• Discretionary income: $94,000 minus $47,587.50 equals $46,412.50
• Blended rate on mixed loans under SAVE: weighted average. $42,000 of undergrad at 5%, $25,000 of grad at 10%.
• Undergrad portion of annual payment: ($42,000 / $67,000) x $46,412.50 x 0.05 equals $1,454.48
• Grad portion of annual payment: ($25,000 / $67,000) x $46,412.50 x 0.10 equals $1,731.54
• Total annual payment: $3,186.02
• Monthly payment: $265.50

PAYE calculation:

• Protection threshold: 1.50 x $21,150 equals $31,725
• Discretionary income: $94,000 minus $31,725 equals $62,275
• Annual payment at 10%: $62,275 x 0.10 equals $6,227.50
• Monthly payment: $518.96

The difference here is $253.46 per month. Over 20 years, assuming static income, that gap compounds to $60,830.40 in additional payments under PAYE.

This borrower should verify SAVE eligibility, confirm both loan types qualify, and model income growth before locking in a plan.

The Cap Rule: When Your IDR Payment Exceeds the Standard Payment

Every IDR plan caps your payment at the standard 10-year repayment amount. This matters at higher incomes.

If your calculated IDR payment exceeds what you would pay on a standard 10-year schedule, the cap applies and you pay the standard amount. At that point, you lose the forgiveness benefit and the interest subsidy, but you still get the plan's other protections.

For the borrower in Example 2, the standard 10-year payment on $67,000 at a blended 5.8% rate is approximately $739 per month. Both SAVE and PAYE produce payments below that cap. The IDR plans are still worth using.

A borrower with the same loans at $180,000 AGI would calculate a SAVE monthly payment of roughly $1,147.50. That exceeds the $739 cap. The cap applies. That borrower is likely better served by standard repayment or refinancing.

How Filing Status Affects Your Payment

Married borrowers who file jointly include both spouses' incomes in the AGI calculation. That inflates the payment.

Filing separately keeps only the primary borrower's income in the calculation. For some couples, this cuts the monthly IDR payment substantially. The tradeoff is the loss of certain tax benefits, including the student loan interest deduction and potentially the child tax credit depending on income.

Run both scenarios. If your IDR payment drops by $300 per month under separate filing, that is $3,600 per year. Compare that against your combined tax liability increase. The math often favors separate filing for borrowers with significant loan balances.

SAVE's Interest Subsidy: A Real Dollar Advantage

SAVE includes a structural advantage that no other IDR plan offers. If your monthly payment does not cover the interest that accrues, the government waives the unpaid interest.

On a $50,000 balance at 6.5% interest, monthly interest accrual is approximately $270.83. If your SAVE payment is $75.48 as in Example 1, you leave $195.35 in interest unpaid each month. Under SAVE, that $195.35 does not add to your principal. Under every other IDR plan, it does.

Over 24 months, that is $4,688.40 in interest that does not capitalize under SAVE. That difference compounds if income remains low.

What Recertification Does to Your Payment

IDR payments recertify annually. Your income from last year's tax return determines next year's payment.

If your income rises 12% between certifications, your discretionary income rises proportionally and your payment increases. The formula does not smooth income spikes. A year with overtime, a bonus, or a freelance project can push your payment up sharply for a full 12-month cycle.

Plan around this. If you expect a high-income year, consider making extra payments during that period rather than treating the required payment as a floor.

When to Stop Running IDR Calculations Manually

The formula is not complex, but the interactions between filing status, household size, loan type mix, income trajectory, and plan eligibility create dozens of variables. A small input error produces a plan selection that costs thousands.

CalcMoney's debt repayment calculator lets you model your exact numbers: AGI, household size, loan balances by type, interest rates, and expected income growth. You see the projected payment, total interest paid, and forgiveness amount across all qualifying plans side by side.

Run your numbers before your next recertification deadline. The difference between the right plan and the default plan is not marginal.

You Might Also Like

• Debt-to-Income Ratio: The Number That Controls Your Mortgage Approval
• How to Calculate Real Savings From a Balance Transfer Offer
• Car Lease vs Buy Calculator: The $15,000 Decision Most People Get Wrong

Calculate your IDR payment across all plans now →