How to calculate total mortgage interest

Estimate lifetime mortgage interest and see how rate, term and extra principal payments change it.

By Calculadoras.Tools Published May 28, 2026 6 min read

When scheduled payments contain only principal and interest:

total interest = payment x number of payments - principal

For $2,000,000 at 9% over 20 years, the payment is approximately $17,994.52; total payments are $4,318,684.59 and interest is $2,318,684.59.

Term	Payment	Total interest
15 years	$20,285.33	$1,651,359.70
20 years	$17,994.52	$2,318,684.59
30 years	$16,092.45	$3,793,282.84

Insurance, fees and taxes are costs but should not be mislabeled as interest. An extra $2,000 per month in the 20-year example could reduce modeled interest to $1,711,832.41 and the term to 186 months, assuming every extra payment reaches principal.

Use the mortgage calculator to generate the full schedule.