The lowest student loan payment is not the cheapest

Every student-loan repayment comparison answers one of two questions, and they have different answers. What can I pay this month, and what will this cost me in the end?

Both are legitimate. A payment you cannot make is not cheap at any total. But it is worth seeing the trade in numbers rather than assuming it away, because the arithmetic is not subtle.

Same balance, same rate, different term

Start with the simplest version, where nothing changes but the number of months. Take a hypothetical $35,000 balance at a hypothetical 6.5%.

• Over 120 months, the hypothetical payment is $397.42 and the total paid is 120 × $397.42 = $47,690.15.
• Over 240 months, the hypothetical payment is $260.95 and the total paid is 240 × $260.95 = $62,628.14.

In that hypothetical the monthly payment falls by $397.42 − $260.95 = $136.47 while the total rises by $62,628.14 − $47,690.15 = $14,937.99. That is the whole trade in two lines: about $136 a month of breathing room, bought for roughly $14,900 across twenty years. Whether that is a good deal depends entirely on what the $136 is doing in the meantime, and nobody but the borrower can weigh that.

Income-driven plans do not have a fixed term

Federal income-driven repayment sets the payment from income and family size rather than from the balance, so the arithmetic above does not carry across directly. The payment is recalculated every year, which means there is no fixed schedule to multiply out.

The plans in force as of 2026 work from discretionary income — income above a multiple of the poverty guideline for the household. IBR takes 10% of income above 150% of the guideline. ICR takes 20% of income above 100%. RAP, the Repayment Assistance Plan effective 1 July 2026, works differently: a percentage of adjusted gross income by band, from 1% to 10%, less $50 per dependent, with a $10 floor. SAVE ended in 2026 after the courts blocked it.

A hypothetical worked through on IBR: a family of two, adjusted gross income $45,000. The 2026 guideline for two people in the 48 contiguous states and DC is $21,640 (91 FR 1797), so 150% of it is 1.5 × $21,640 = $32,460. Discretionary income is $45,000 − $32,460 = $12,540, and the IBR payment is $12,540 × 10% ÷ 12 = $104.50 a month.

The line that decides whether the balance grows

This is the number nobody prints next to the payment, and it is the one that explains a balance going up while payments are being made on time.

Interest on that hypothetical $35,000 at 6.5% is $35,000 × 6.5% ÷ 12 = $189.58 a month. The IBR payment above is $104.50. The difference, $189.58 − $104.50 = $85.08 a month, is interest the payment did not reach, and in most plans it is added to what is owed.

That is not a mistake and it is not a failure. It is what an income-driven plan is for: the payment tracks what a household can pay, not what the balance demands. But it means "total paid" and "balance at the end" are separate questions, and forgiveness at the end of the plan term — or under Public Service Loan Forgiveness — is what resolves the gap for many borrowers. The terms, and the tax treatment of forgiven amounts, are set by the plan and by current law, so confirm both with your servicer rather than with a calculator.

The tool

RepaySmart takes income, balance, interest rate, family size and region, and prints the estimated monthly payment under the Standard 10-year plan, IBR, ICR and RAP side by side, along with the discretionary-income figure the income-driven ones are built from, using the 2026 guideline.

It compares monthly payments, which is what the formulas define cleanly. It does not compute lifetime cost, forgiveness timelines or PSLF eligibility — those need the plan term and your own history, and it does not guess at either. RAP's bracket arithmetic was still settling through 2026, so treat that line in particular as an estimate and confirm it with your servicer. Nothing here is financial advice, and no plan here is being recommended over another.