Student loans: federal first, snowball second.

1. Federal vs private: the binary that matters

US student loans come in two structurally different forms. Federal loans (Direct Subsidised, Direct Unsubsidised, Direct PLUS, Perkins where still applicable) are issued or guaranteed by the US Department of Education and carry a suite of borrower protections: Income-Driven Repayment plans that cap monthly payments by income, deferment and forbearance options, Public Service Loan Forgiveness (PSLF), Teacher Loan Forgiveness, and several other forgiveness programmes. Federal loans also typically carry lower fixed APRs than private loans.

Private loans (issued by Sallie Mae, Discover, banks, credit unions, refinancing-startups) are commercial debt with no statutory borrower protections beyond standard consumer-debt law. APRs can be fixed or variable, often higher than federal. They have no IDR plans, no PSLF eligibility, and limited forbearance. They are, in payoff terms, more like personal loans than like federal student loans.

Implication for snowball or avalanche: never refinance a federal loan into a private loan to chase a marginally lower rate without understanding what you are giving up. The federal protections often outweigh a 1–2 percentage-point rate saving.

2. The repayment-plan decision precedes the payoff method

Federal Direct Loans default to the Standard 10-year Repayment Plan. This is the right plan if you can comfortably afford the standard payment and want to clear the debt fastest. It is the wrong plan if your income is low relative to your loan balance — in which case an Income-Driven Repayment plan (currently SAVE, PAYE, IBR, or ICR depending on enactment status) caps monthly payments at 10–20 % of discretionary income and forgives any remaining balance after 20–25 years (subject to taxable-income treatment of forgiven balance under federal law as of the policy regime in effect at forgiveness).

The decision tree: if your federal loan balance is less than your annual income, the Standard plan and an aggressive payoff is usually right. If your balance exceeds 1.5× your annual income, an IDR plan with optional extra payments is usually right. The avalanche/snowball method then operates on the cash you choose to direct above the IDR-required minimum.

3. Public Service Loan Forgiveness (PSLF)

If you work for a qualifying public-service employer (US federal, state, local, tribal government; 501(c)(3) non-profit), federal Direct Loans on an IDR plan are eligible for forgiveness after 120 qualifying monthly payments (10 years). The forgiven balance is not taxable under current law. For borrowers in qualifying employment, PSLF transforms the debt-payoff calculus: the optimal strategy is to pay the IDR minimum (which is usually the lowest possible payment) for 120 months, not to pay extra. Paying extra reduces the eventual forgiveness benefit, dollar-for-dollar.

Implication: borrowers in PSLF-eligible employment should typically exclude federal student loans from any snowball or avalanche plan and direct the extra payments toward non-federal debt or savings instead. The calculator on this site is a tool for the post-IDR-decision step, not the IDR decision itself. Verify PSLF eligibility annually using the official PSLF Help Tool at studentaid.gov.

4. The interest-subsidy nuance

Direct Subsidised Loans (issued to undergraduate borrowers based on financial need) have a structural feature worth understanding: the federal government pays the interest while the borrower is in school at least half-time, in the 6-month grace period after graduation, and during qualifying deferment periods. After the grace period ends, the loan accrues interest like any other.

Direct Unsubsidised Loans accrue interest from the day of disbursement. Borrowers who don’t pay the in-school interest see it capitalise (added to principal) at repayment start, increasing the effective balance. For unsubsidised borrowers still in school, paying the in-school interest as it accrues — even modest amounts — can save thousands in capitalised interest over the life of the loan.

5. Worked example: refinancing federal to private

A borrower carries $42,000 of federal Direct Unsubsidised at 6.5 % (issued 2022 for a graduate programme), with a Standard 10-year payment of approximately $476/month. A private refinancer offers 5.2 % fixed for a 10-year term, payment approximately $448/month. Lifetime interest savings: approximately $3,300.

What the borrower gives up by refinancing: PSLF eligibility, IDR access, statutory deferment and forbearance options, and forgiveness of remaining balance after 20–25 years on IDR. For a borrower with stable employment and no PSLF prospect, the $3,300 saving is real. For a borrower whose career trajectory might include public-sector or non-profit work, the saving is a bad trade. The decision is not just the rate differential; it is the optionality value of the federal protections, which is substantial and difficult to replace once lost.

6. Integrating student loans into snowball/avalanche

For non-PSLF borrowers on the Standard plan with no plan to switch to IDR, federal student loans can be included in the calculator alongside other debts. Use the federal APR (typically 4.5–7.5 %) and the Standard monthly payment as the minimum. The avalanche method will typically place credit-card debt above student loans (higher APR) and student loans above an auto loan (typically 6–9 %); the snowball method will order purely by balance.

For private student loans, treat them like personal loans: APR, balance, and minimum go into the calculator at face value. There are no special protections to preserve. Snowball or avalanche operate normally.

7. The forbearance trap

Federal student loans offer forbearance — a temporary pause in payments — as a borrower-protective feature for households facing hardship. The trap: interest continues to accrue during forbearance, and on most plans the accrued interest capitalises into principal when forbearance ends, increasing the effective debt burden permanently. Deferment is similar but, for subsidised loans only, the federal government covers the interest during the deferment period.

Use forbearance only when truly necessary, and only as briefly as possible. If hardship is the issue, switching to an IDR plan with a $0 monthly payment under low-income calculation often produces a better outcome than forbearance — because IDR months count toward the 20-25 year forgiveness clock and the 120-month PSLF clock, while forbearance months typically do not.