Student Loan Calculator

How it works

Separating school borrowing from repayment

Borrowing during school and repaying an existing student loan are different stages. Choose the mode that matches the balance and timing you know. The repayment-budget mode works backward from a payment, while fixed-payment payoff estimates how long a balance takes to clear. These scenarios follow the stated loan model and do not automatically reproduce income-based repayment or forgiveness programs.

Standard repayment: formula and assumptions

Deferred simple interest = balance×annual rate×months/12. Capitalize it once, then amortize the new balance.

This is standard fixed-rate repayment. Eligibility, federal income-driven plans, forgiveness, and capitalization rules require current program-specific guidance.

Borrowing during school & repayment: formula and assumptions

Delay interest for a tranche = principal × annual rate × months outstanding / 12.

Annual borrowing starts each school year. The model keeps unpaid interest separate unless capitalization is selected. A numerical repayment schedule pays interest before principal without charging interest on a separate unpaid-interest bucket.

Loan principal from repayment budget: formula and assumptions

Principal = monthly payment × annuity present-value factor.

Solves interest-bearing principal from a monthly repayment budget, with no separate unpaid-interest balance, fees or future borrowing.

Fixed-payment payoff: formula and assumptions

Payoff months = −ln(1−Pr/payment) / ln(1+r).

The monthly payment must exceed the interest due. The final installment is reduced to the remaining balance.

Worked example

Reference example currency: USD. These fixed examples do not change with your calculator preferences.

Using the Standard repayment example:

Current loan balance ($)

30000

Annual effective return (%)

5

Repayment term

10

Months before repayment

0

Interest during deferment

Accrues (simple interest)

Extra monthly payment ($)

0

Deferred simple interest = balance×annual rate×months/12. Capitalize it once, then amortize the new balance.

Example result

These are illustrative inputs. Change the values to explore a different scenario.

What to keep in mind

Federal program changes are not modeled as guessed repayment rules.

Formula references

• Federal Student Aid: repayment (opens in a new tab)

References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.

Common questions