Personal Loan Calculator

Use this personal loan calculator to estimate your monthly payment, total interest, total cost, and payoff date, including origination fees. You can also add extra payments or a lump sum to see how much time and interest you could save.

How to use our Personal Loan Calculator

1. Enter your loan amount (the starting balance before any fees).
2. Enter the interest rate (APR percent) from your offer.
3. Enter the loan term in months (for example, 36 for 3 years).
4. Pick your first payment date to get calendar payoff dates.
5. Open Advanced options if your loan has an origination fee, then choose the fee type (percent or USD) and enter the fee.
6. In Advanced options, choose the origination fee treatment: deducted from cash received or financed (added to the balance).
7. If you plan to pay extra, enter an extra monthly payment and when it starts (payment number).
8. If you will make a one-time extra payment, enter the lump sum amount and the payment number to apply it.
9. Click Calculate to see your scheduled payment, total interest, cash received, effective APR with fees, payoff dates, and the amortization schedule.

Definitions

APR (annual percentage rate): The yearly interest rate shown as a percent. This calculator turns it into a monthly rate for monthly payments.

Amortization: A payoff process where each payment covers interest first, then reduces the balance (principal). Early payments usually have more interest. [1]

Origination fee: An upfront fee some lenders charge to make the loan. It can be a percent of the loan amount or a flat dollar amount. [2]

Financed fee (added to balance): The fee is added to the balance you repay, which can raise the payment and total interest.

Deducted from proceeds (cash received): The fee is taken out of the money you get, so you receive less cash but your starting balance stays the same.

Effective APR including fees: An APR-like rate computed from the cash you actually receive and the payment schedule, so you can compare offers when fees apply. [4]

Extra payment: Extra money you choose to pay on top of the scheduled payment, applied to principal after that months interest.

Methodology

Inputs and setup

This calculator assumes a fixed-rate personal loan with monthly payments and a standard amortization process. [1]

monthly_rate = apr_percent / 100 / 12

fee_amount = (orig_fee_type == "Percent") ? loan_amount * (orig_fee_value/100) : orig_fee_value

principal_financed = loan_amount + (fee_treatment == "Financed" ? fee_amount : 0)

cash_received = loan_amount - (fee_treatment == "Deducted" ? fee_amount : 0)

Validation and edge cases

Required inputs must be valid: loan amount must be greater than 0, APR percent must be present and at least 0, term months must be a whole number at least 1, and first payment date must be selected to compute payoff dates.

If the fee treatment is deducted from proceeds, the fee amount must be less than the loan amount so cash received stays positive. If not, the calculator shows an error.

If APR is 0, interest is 0 and the payment is a simple divide (shown below). Extra payment fields can be 0. If extra payments start after the last payment, the calculator treats it as no extra payments and shows a warning message (results still compute).

Scheduled monthly payment (base plan)

payment = principal_financed * monthly_rate / (1 - (1 + monthly_rate)^(-term_months))

if monthly_rate = 0, payment = principal_financed / term_months

The scheduled payment is computed from the financed balance, so financing a fee can increase the payment and total interest. [4]

Amortization loop (base plan and extra-payment plan)

For each payment number i, interest is computed on the prior balance, then the rest of the payment reduces principal. Extra monthly payments and a lump sum are applied after interest for that month. The final payment is reduced so the balance does not go below zero. [1]

interest_i = balance_{i-1} * monthly_rate

scheduled_principal_i = payment - interest_i

extra_i = (i >= extra_start ? extra_monthly : 0) + (i == lump_sum_number ? lump_sum_amount : 0)

principal_paid_i = min(balance_{i-1}, scheduled_principal_i + extra_i)

balance_i = balance_{i-1} - principal_paid_i

If at any point the scheduled payment is not enough to cover that months interest (payment is less than or equal to interest), the loan would not amortize. In that case, interest and payoff outputs are shown as N/A with an error message so you can fix the inputs.

Totals and first-payment interest

Total interest is the sum of all monthly interest amounts. Total of payments is the sum of scheduled payments actually made (including the smaller final payment if payoff happens early with extra payments).

first_payment_interest = starting_balance * monthly_rate

The starting balance for the base plan is principal_financed (which includes a financed fee, if selected).

Payoff date (calendar estimate)

The payoff date is estimated by advancing the first payment date by the number of payments made minus 1, keeping the same day-of-month when possible.

payoff_date = first_payment_date + (payments_made - 1) months

Effective APR including origination fee

This tool computes an APR-like annual rate that makes the present value of the base-plan payments equal the net cash you actually receive (cash_received). This helps compare loans when fees change the real cost. [4]

Find r such that: cash_received = sum_{i=1..N} payment / (1 + r)^(i/12)

The solver uses bisection on r (an annual rate) and reports effective_apr = r*100. If the fee is 0, the effective APR should match the input APR up to rounding. If the solver cannot converge, the effective APR is shown as N/A with a note to double-check fee settings.

Sources