TL;DR
For a fast, private answer, use the Calc Garden mortgage calculator. It shows your monthly payment, total repaid and total interest as three clear figures, is completely free with no sign-up, and never sends your numbers anywhere. If you also need US property tax, insurance and PMI in the estimate, NerdWallet or SmartAsset show total interest too and add those fields.
What "shows total interest" actually means
Total interest is the sum of every interest charge across the life of the loan, not the rate and not the monthly payment. It is the number that tells you how much the borrowing itself costs on top of the amount you borrowed. Many calculators lead with the monthly payment because it is the smaller, friendlier figure, then hide total interest inside an expandable amortization table. A calculator that shows total interest up front lets you judge the true cost of a longer term or a higher rate at a glance.
How to read total interest in five steps
- Open the mortgage calculator; it loads with sensible defaults already populated.
- Enter your loan amount, the amount you are borrowing.
- Enter the annual interest rate and the term in years.
- Read the monthly payment, total repaid and total interest, which update live as you type.
- Compare scenarios by nudging the term up or down and watching total interest move, since that is where the biggest swings hide.
Which free tool shows total interest best
All three options below show total interest somewhere. The difference is how quickly you reach it and what the tool asks of you to get there. Pricing reflects each product as of 2026.
| Feature | Calc Garden | NerdWallet | SmartAsset |
|---|---|---|---|
| Total interest shown | Up front | In breakdown | In breakdown |
| Total repaid shown | Yes | Yes | Yes |
| Price (as of 2026) | $0, no signup | $0, ad-supported | $0, lead-funded |
| No ads or quote prompts | Yes | No | Partial |
| Inputs stay in your browser | Yes | Partial | Partial |
| US tax, insurance and PMI fields | No | Yes | Yes |
Calc Garden puts total interest on the first screen with no clutter. NerdWallet and SmartAsset hold the lifetime interest figure inside a fuller amortization view and are the better choice if you also need a US escrow estimate, since both are free and US-localised.
Go deeper than the headline number
Once you have your total interest, two related tools help you act on it. The loan amortization calculator shows how each payment splits between principal and interest over time, so you can see how overpaying early cuts total interest. The FIRE retirement calculator helps you weigh paying a mortgage down faster against investing the same money. For a broader comparison of free options, see our free alternative to NerdWallet and SmartAsset calculators and the full guides index.