Loan Calculator

Use this loan calculator to estimate your payment, total interest, total cost, and payoff date for a fixed-rate loan, with options for extra payments and an origination fee. It also estimates an effective APR with fees so you can compare offers more fairly.

How to use our Loan Calculator

1. Enter the Loan amount (USD): the amount you want to borrow.
2. Enter the Annual interest rate (percent) shown for the loan (for example, enter 6.5 for 6.5%).
3. Enter the Loan term (years): how long you plan to take to pay it back.
4. Choose a Payment frequency (Monthly, Biweekly, or Weekly).
5. Pick the First payment date to get a calendar payoff date.
6. Open Advanced options to add an Extra payment each period (USD) if you want to pay down the loan faster.
7. In Advanced options, enter an Origination fee (USD) and choose how it is treated (Paid upfront or Rolled into loan).
8. Click Calculate. Review the scheduled payment, total interest, total paid, payoff date, and how much time and interest extra payments save.

Definitions

Principal: The amount you still owe on the loan balance (not counting future interest).

Interest: The cost of borrowing money, calculated each payment period from the remaining balance.

Annual interest rate: The yearly rate used to compute interest (this calculator divides it by payments per year to get a per-payment rate).

APR (annual percentage rate): A yearly cost measure that can include some fees. This page also shows an effective APR estimate from cash flows when you add an origination fee.

Amortization: Paying a loan off over time with regular payments, where early payments usually include more interest and later payments include more principal.

Origination fee: A one-time lender fee charged to start the loan.

Paid upfront (fee): You pay the fee at the start, so you receive less cash than the loan amount.

Rolled into loan (fee): The fee is added to the balance, so you borrow the fee too and pay interest on it.

Extra payment: Optional extra money added each period to reduce the balance faster (often saves interest).

Methodology

What this calculator assumes

This is a fixed-rate installment loan model using standard amortization math and a period-by-period payoff schedule, similar to common loan amortization implementations.[1]

Interest is computed from the remaining balance each period using a simple periodic rate (annual rate divided by payments per year). Some lenders use different conventions, so your final cents may differ.

Step 1: Convert inputs to a per-payment setup

payments_per_year = 12 (Monthly) or 26 (Biweekly) or 52 (Weekly)

rate_per_period = (annual_rate_percent / 100) / payments_per_year

n = term_years * payments_per_year

If n is not positive, the calculator blocks the result and asks you to fix the term.

Step 2: Apply origination fee treatment

financed_principal = loan_amount + (fee_treatment == "Rolled into loan" ? origination_fee : 0)

net_cash_to_borrower = loan_amount - (fee_treatment == "Paid upfront" ? origination_fee : 0)

Total paid includes principal and interest payments, plus any origination fee that is paid upfront (because that is still money you paid).

Step 3: Compute the scheduled payment (without extra)

payment = financed_principal * r / (1 - (1 + r)^(-n))

if r = 0 then payment = financed_principal / n

Here, r means rate_per_period. The output "Scheduled payment per period" is this payment (it does not include your optional extra payment).

Step 4: Build the payoff schedule (amortization)

For each period i, the calculator updates interest, principal paid, and remaining balance. If rounding is enabled, it rounds interest to the nearest cent each period before updating the balance.

interest_i = balance_(i-1) * r

principal_paid_i = payment_i - interest_i

balance_i = balance_(i-1) - principal_paid_i

The actual payment for a period is normally:

payment_i = scheduled_payment + extra_payment

If extra payments would make the balance go below zero, the calculator follows your selection: either it reduces the final payment to exactly pay off, or it allows an overpay amount (shown as a note). The schedule stops at payoff, so the "Number of payments" can be less than n.

Step 5: Payoff date from the first payment date

The payoff date is computed by adding the number of payment periods (minus 1) to your first payment date, using your chosen frequency. The result is shown as an estimated calendar month of the last payment.

Step 6: Interest saved and time saved vs no extra payments

The calculator runs a second scenario with the same inputs but extra_payment = 0, then compares totals:

interest_saved = total_interest_no_extra - total_interest_with_extra

time_saved_months = (payments_no_extra - payments_with_extra) * (12 / payments_per_year)

Step 7: Effective APR estimate (with fees)

This estimates a yearly rate from cash flows: you receive net_cash_to_borrower at the start and you repay the actual payments over time. It solves for the per-period rate that makes the present value of payments match what you received, then converts to an annual percent.

Find r_eff_per_period such that net_cash_to_borrower = sum_{i=1..k} (payment_i / (1 + r_eff_per_period)^i)

effective_apr_percent = r_eff_per_period * payments_per_year * 100

The solver uses a safe bisection search and returns N/A if net_cash_to_borrower is not positive (for example, a paid-upfront fee that is too large).

Notes and validation

The calculator blocks invalid inputs (like negative amounts, missing date, or a non-positive term). It also caps iterations and treats tiny leftover balances near zero as paid off to avoid endless loops when rounding is enabled.[1]

Sources