Calculator Methodology

How the student loan model works, what assumptions drive outputs, and what this tool does not attempt to do.

What the Model Includes

Plan comparisons: RAP, PAYE, New IBR, Old IBR, Standard 10-Year, Refi, and PSLF-style path.
Marital status and filing-status behavior with borrower/spouse income and debt context.
Time-series outputs for payment and balance through up to 30 years.

Core Assumptions

Income growth defaults to 3% annually unless manual values are entered.
RAP is modeled with AGI-based tiers, a $10/month minimum, and a $50/month reduction per dependent.
Refi auto mode defaults to a conservative 7.25% over 10 years.
Forgiveness tax handling is modeled as an estimated future marginal tax rate input.
Poverty/discretionary calculations use simplified annualized thresholds for planning.

Benchmark Scenarios We Use

Scenario A: Single borrower, $200,000 federal debt, $208,000 AGI, 6.8% loan rate. Checks that plan ranking remains directionally stable across repayment modes.
Scenario B: Married filing jointly, spouse income + spouse debt included. Checks apportionment behavior and IDR sensitivity to household income basis.
Scenario C: Public-service toggle on with 10-year horizon. Checks that PSLF path resolves without forgiveness-tax add-on.

Known Limitations

This is not a legal or tax engine and does not replace individualized professional advice.
Program rules and servicer execution can change over time.
Exact federal implementation details can differ from simplified planning assumptions.

How to Use Responsibly

Use this model to compare directionally, not to overfit exact dollar precision.
Run multiple scenarios with conservative inputs before making long-term commitments.
Pair results with documentation from your loan servicer and tax professional.

Attribution

We credit Student Loan Planner for helping establish a high-utility public calculator model: studentloanplanner.com .
We follow Adam S. Minsky's borrower-focused policy coverage on Forbes: forbes.com/sites/adamminsky .

Student Loan Legislation Watch: OBBBA Timeline

We maintain a date-stamped policy view because federal loan rules can move quickly. The timeline below reflects published federal sources and should be treated as informational, not legal advice.

July 4, 2025: The One Big Beautiful Bill Act (OBBBA), Public Law 119-21, was signed into law.
July 18, 2025: ED announced implementation steps and issued guidance indicating some provisions had immediate effect.
July 1, 2026: Major repayment-structure changes begin for new borrowers under the law's framework.
July 1, 2027: Additional provision changes take effect for loans made on or after this date (including deferment and rehabilitation rule changes described in federal summaries).
June 30, 2028 / July 1, 2028: Transition boundary for borrowers in plans phased out by OBBBA.

OBBBA Changes Most Relevant to This Calculator

New borrowing limits: Professional borrowers are generally modeled at a $50,000 annual cap and $200,000 aggregate cap; graduate non-professional borrowers at $20,500 annual and $100,000 aggregate.
Overall lifetime cap: The statute sets a $257,500 lifetime borrowing limit across federal loan types for an individual borrower (excluding Parent PLUS borrowed as a parent).
Parent PLUS compression: Parent PLUS is limited to $20,000 annual and $65,000 lifetime per dependent student.
Repayment structure shift: New loans move to a simplified plan set (Standard + RAP), while legacy-plan availability follows a statutory transition schedule.
Grad PLUS sunset for new borrowers: Federal summaries indicate phaseout with a transition path for currently enrolled borrowers under specified conditions.

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