How does a student loan calculator work?

A student loan calculator compares federal or private university debt under the Standard 10-Year repayment structure against Income-Driven Repayment (IDR) options like SAVE, standard ICR, or IBR plans.

What is an Income-Driven Repayment (IDR) plan?

An IDR plan is a federal student loan repayment plan that caps your monthly payment at a set percentage (typically 5% to 10%) of your "discretionary income," which is the portion of your Adjusted Gross Income (AGI) that exceeds a percentage of the Federal Poverty Level.

What is Discretionary Income for student loans?

For federal repayment plans, discretionary income is the difference between your Adjusted Gross Income (AGI) and a set percentage of the Federal Poverty Guidelines for your family size (for example, the SAVE plan uses 225% of the Poverty Level, while older plans like IBR use 150%).

How can student loan interest subsidization help me?

On certain federal plans (like SAVE), if your calculated income-driven payment is less than the monthly interest that accumulates, the government waives the remaining interest. This prevents your overall balance from growing (negative amortization).

What is the standard interest rate on federal student loans?

Federal student loan interest rates are fixed and set annually by Congress. For undergraduate loans, historical rates typically range from **4% to 6.5%**, while graduate loans and Parent PLUS loans carrying higher rates ranging from **7% to 9.5%**.

Can student loans be forgiven?

Yes. Under federal income-driven plans, any remaining balance is forgiven after **20 to 25 years** of consistent payments. Additionally, the Public Service Loan Forgiveness (PSLF) program offers tax-free forgiveness after just **10 years (120 payments)** for qualifiers.

Student Loan Repayment Calculator

Compare federal and private university debt repayment strategies. Input your loan balance alongside your Adjusted Gross Income (AGI) to run side-by-side simulations of standard fixed vs. federal income-driven repayment plans.

University Debt details

Total Student Loan Balance ($)

Debt Balance Slider $40,000

Interest Rate (%)

Repayment Term (Years)

Federal IDR Plan Parameters (Optional)

Adjusted Gross Income (AGI) ($)

Family Size

Repayment Plans comparison

Standard Plan Monthly Payment

$440.12

Standard Repayment Term	10 Years
Total Standard Interest Paid	+$12,814.40
Total Standard Repayment Payout	$52,814.40
Federal IDR Plan Estimate (SAVE/IBR Limit) Simulated IDR Monthly Payment $134.29 Based on discretionary income exceeding 225% of FPL ($33,885 single threshold deduction).

● Loan Principal (76.0%) ● Total Interest paid (24.0%)

Calculating College Repayments & IDR Eligibility

The mathematics defining student loan repayment plans offer deep financial modeling across multiple structural strategies:

Standard Fixed Monthly Amortization: Modeled using the base geometric lending annuity equation:
Payment = Loan Balance * [r(1+r)^n] / [(1+r)^n - 1] Where r is periodic interest rate (interest rate / 12 / 100) and n is term payments (Years * 12).
Federal IDR SAVE Plan: Caps your monthly payment at exactly 10% of discretionary earnings above 225% of federal poverty guidelines:
SAVE threshold = Guidelines 100% value * Family Size multipliers * 2.25
Discretionary Earnings = Max(0, AGI - SAVE threshold)
SAVE Payment = (Discretionary Earnings * 0.10) / 12

Worked Step-by-Step Repayment Example

Suppose an undergraduate graduates with **$40,000.00** in federal student loans at a **5.8% interest rate**, earning an annual Ajusted Gross Income (AGI) of **$50,000.00** as a **single filer**:

Repayment Scheme Comparisons

Total student loan principal: $40,000.00
Interest rate: 5.8%
Standard 10-Year Repayment EMI:
[$40,000 * 0.004833 * (1.004833)^120] / [(1.004833)^120 - 1] = $440.12 monthly
Lifetime Interest: ($440.12 * 120) - $40,000 = $12,814.40
Standard federal single single-person poverty baseline in 2024/2025: $15,060.00
SAVE Plan Deduction Threshold (225% of $15,060): $15,060.00 * 2.25 = $33,885.00
Filer discretionary income: $50,000 AGI - $33,885 SAVE threshold = $16,115.00
Calculated Federal SAVE plan payment (10% limit):
($16,115.00 discretionary * 10%) / 12 = $134.29 monthly
Repayment savings: Utilizing SAVE lowers the immediate monthly payment burden by **$305.83** compared to the standard flat 10-year option.

Frequently Asked Questions — Student Loans

Verified & Reviewed by Michael Carter, Senior Financial Content Specialist & Personal Finance Research Analyst

Michael Carter is a Financial Content Specialist at Findensity, where he researches and writes about personal finance, banking, credit cards, investing, insurance, taxes, loans, and financial planning. His work focuses on simplifying complex financial topics into clear, actionable guidance that helps readers make informed money decisions.

Professional Advice Disclaimer: Results from this calculator are purely statistical representations intended as informative educational references. Federal student loan criteria, poverty thresholds, and income-driven SAVE regulations are subject to ongoing political and judicial review. Please consult a qualified college loans expert or professional financial planner.