Loan Calculator
Calculate monthly payments, total interest, and view a complete amortization schedule for any fixed-rate loan. Works for mortgages, auto loans, personal loans, and more.
What Is a Loan Calculator?
A loan calculator is a financial tool that computes your monthly payment, total interest, and total cost for a fixed-rate loan using the standard amortization formula. Whether you’re taking out a mortgage, auto loan, personal loan, or student loan, knowing your monthly payment before you commit is essential for budgeting and comparing offers from different lenders. The calculator uses the formula M = P * [r(1+r)^n] / [(1+r)^n - 1], where P is the principal (amount borrowed), r is the monthly interest rate, and n is the total number of payments.
TweakFiles Loan Calculator runs entirely in your browser with no server processing — your financial information is never transmitted or stored anywhere. Unlike bank websites that require account creation, or financial apps that track your data, this calculator provides instant results with complete privacy. Enter your loan amount, interest rate, and term to see exactly what you’ll pay each month and over the life of the loan.
Understanding Amortization
Amortization is the process of spreading loan payments over time so that each payment covers both interest on the remaining balance and a portion of the principal. In the early years of a loan, most of your payment goes toward interest because the outstanding balance is large. As you pay down the principal, the interest portion shrinks and more of each payment goes toward principal. This is why a 30-year mortgage borrower pays significantly more total interest than a 15-year borrower — the longer term means more months of interest accumulating on a larger balance.
How Interest Rate Affects Your Payment
Even small changes in interest rate can dramatically affect your total cost. On a $300,000 mortgage, the difference between 6.0% and 6.5% APR over 30 years is approximately $36,000 in additional interest — about $100 more per month. This is why shopping for the best rate and understanding rate locks, points, and APR vs. interest rate distinctions is so important. Use this calculator to compare scenarios side by side: adjust the rate by 0.25% increments to see exactly how much each quarter-point costs you over the life of the loan.
How to Calculate Your Loan Payment in 3 Steps
Enter Loan Details
Input the total loan amount (principal), the annual interest rate quoted by your lender, and the loan term in years. For mortgages, common terms are 15 or 30 years. For auto loans, 3 to 7 years is typical. For personal loans, 1 to 5 years. The calculator accepts any combination — you can model unconventional terms like 20-year mortgages or 10-year student loan repayment plans.
View Your Results
Click "Calculate" to see your monthly payment, total payment over the life of the loan, and total interest paid. The monthly payment is calculated using the standard amortization formula used by banks and lenders worldwide. Results appear instantly with no server processing or wait time.
Review the Amortization Schedule
Scroll down to see a month-by-month breakdown of every payment, showing how much goes to principal vs. interest, and your remaining balance after each payment. The first 12 months are shown by default — click "Show all" to see the complete schedule. Use this to understand when your loan crosses the halfway point, or to plan extra payments.
TweakFiles vs Other Loan Calculators (2026)
A comparison of popular loan calculator tools available online in 2026.
| Feature | TweakFiles | Bankrate | NerdWallet | Calculator.net |
|---|---|---|---|---|
| Price | Free forever | Free (with ads) | Free (with ads) | Free (with ads) |
| Signup Required | Never | No | For comparisons | No |
| Ads | None | Heavy (sponsored lenders) | Heavy (affiliate links) | Heavy ads |
| Privacy | 100% client-side | Data tracked | Data tracked | Data tracked |
| Amortization Schedule | Full schedule | Yes | Yes | Yes |
| Mobile Friendly | Yes | Yes | Yes | Partial |
| Data Selling | Never (no data collected) | May share with lenders | May share with partners | Unknown |