Bank Loan Calculator
Before you accept a loan offer from a bank, you need to know exactly how much you’ll pay each month and over the entire term. A bank loan calculator turns the loan amount, interest rate, and term into clear numbers: monthly payment, total interest, and the final cost. This free tool supports both annuity (equal installments) and differentiated (decreasing) payment schedules – so you can compare real scenarios, not just advertised rates.
What Your Loan Payment Consists Of
Each monthly installment is split into two parts: interest charged on the outstanding balance and a principal repayment that reduces your debt. In the early months of a loan, interest dominates the payment. Over time, the principal portion grows while the interest portion shrinks. The calculator above automatically builds an amortization table that shows this shift month by month.
Annuity vs. Differentiated Payments: Which One Costs Less?
Banks typically offer two repayment structures, and the choice can alter your total cost by hundreds of dollars.
- Annuity (equal payments). You pay the same amount every month. Early payments are mostly interest, so the principal decreases slowly. This method is easier to budget but generates higher total interest.
- Differentiated (decreasing payments). The principal is repaid in equal chunks, and interest is calculated only on the remaining balance. Monthly payments start higher and gradually decline. Total interest is lower because you reduce the principal faster.
Example for a $10,000 loan over 1 year at 12% annual rate:
- Annuity: monthly payment $888.49, total interest $661.87.
- Differentiated: first payment $933.33, last payment $841.67, total interest $650.00.
The difference of $11.87 may seem small, but on a $250,000 mortgage over 20 years it grows to thousands of dollars. Use the calculator to test both options with your real figures.
The Math Behind the Calculator
For annuity loans, the calculator relies on the following formula to determine your fixed monthly payment:
P = (S × i × (1 + i)^n) / ((1 + i)^n − 1)
Where:
- P – monthly payment
- S – total loan amount (principal)
- i – monthly interest rate (annual rate ÷ 12)
- n – total number of months
Plug in a $15,000 loan for 3 years at 9% APR:
- i = 0.09 ÷ 12 = 0.0075
- n = 36
- P = (15000 × 0.0075 × (1.0075)^36) / ((1.0075)^36 − 1) ≈ $476.89
Over 36 months you’ll pay 476.89 × 36 = $17,168.04, which means $2,168.04 in interest.
Differentiated payments are simpler: divide the principal by the number of months (15000 ÷ 36 = $416.67 principal per month) and add interest on the remaining balance. The first payment includes interest of 15000 × 0.0075 = $112.50, so the total first payment is $529.17. Each subsequent month the interest decreases by about $3.13.
How a Loan Calculator Protects You from Overpaying
Even small adjustments to the loan parameters can lead to meaningful savings. The calculator lets you experiment instantly:
- Term length. Extending a $20,000 loan from 3 to 5 years at 7% APR raises total interest from $2,236 to $3,723 – a 66% increase. See the trade-off between lower monthly payments and higher overall cost before you commit.
- Rate shopping. A 1‑percentage‑point drop on a $25,000 4‑year loan (from 10% to 9%) saves $576 in interest. Run two scenarios side by side and pick the lender with the better real‑world offer.
- Extra payments. If your calculator allows it, add a $50 monthly overpayment. On a $12,000 loan at 11% for 4 years, those extra payments cut the term by 9 months and shave off $210 in interest.
As of 2026, average unsecured personal loan rates range from 6% to 36% depending on credit score, while secured loans may start lower. Always verify the exact APR with the bank and include any origination fees or insurance in your total cost estimate.
This calculator provides mathematical estimates only and does not constitute financial advice. Loan terms, eligibility, and final costs vary by lender.