Student Loan Calculator
$
5.00%
10 yrs
6 mos
Monthly Payment$326.15
Total Interest$9,138.18
Total Cost$39,138.18
Interest Accrued During Grace$750.00
total cost$39.1K
Principal$30,000.00
Interest$8,388.18
Grace Interest$750.00
Student loans often accrue interest during a grace period before repayment begins, which quietly raises the balance you eventually amortize. This calculator first adds simple interest over the grace months to your original loan, then treats that larger balance as the principal for a standard fixed-rate repayment schedule. It returns your monthly payment, the total interest, and the full lifetime cost.
Formula
Pe = L(1 + i·g); M = Pe · i(1 + i)^n / ((1 + i)^n − 1)
- L
- Original loan amount
- i
- Monthly interest rate = annual rate ÷ 12 ÷ 100
- g
- Grace-period months during which interest accrues
- Pe
- Effective principal = loan plus accrued grace interest
- n
- Number of payments = term in years × 12
How it works
- Enter the loan amount, the annual interest rate, the repayment term in years, and the number of grace-period months before payments start.
- The calculator computes interest accrued during the grace period as loan × monthly rate × grace months, and adds it to the loan to form the effective principal.
- It amortizes that effective principal with the standard fixed-payment loan formula over your term, then reports the monthly payment, total interest, and total cost.
Worked example
A $30,000 loan at 5.5% for a 10-year term with a 6-month grace period.
- Monthly rate i = 5.5 ÷ 12 ÷ 100 = 0.00458333.
- Grace interest: 30,000 × 0.00458333 × 6 = $825, so the effective principal is $30,825.
- Amortize $30,825 over 120 months: monthly payment ≈ $334.53.
- Total cost: 334.53 × 120 = $40,143.87; total interest: 40,143.87 − 30,000 = $10,143.87.
Monthly payment about $334.53, total interest about $10,143.87, and total cost about $40,143.87.
Frequently asked questions
- Why is the total interest higher than rate times principal would suggest?
- Two things add up: interest that accrues during the grace period is capitalized into the balance, and the loan is then amortized so you pay interest on the slowly declining principal over the whole term.
- Does this model federal income-driven repayment plans?
- No. It assumes a standard fixed monthly payment over the term you choose. Income-driven plans tie payments to your earnings and can change over time, so their totals will differ from this estimate.
- What if my loan does not accrue interest during the grace period?
- Subsidized federal loans typically do not accrue interest while in school or during the grace period. Set the grace months to zero so the effective principal equals your original loan amount.