How interest-only loan calculator works
An interest-only loan lets you pay only the interest for an initial period, so your monthly payment is lower but your principal never goes down. After that period ends, the loan converts to a standard amortizing loan and you pay both principal and interest, usually at a higher payment to pay the balance off within the remaining term.
Enter the loan amount, the interest rate, the length of the interest-only period (in years), and the length of the amortization period that follows. The calculator computes the interest-only monthly payment (principal times the monthly rate), the total interest paid during that period, then the amortizing monthly payment and its total interest using the standard amortization formula.
The totals combine both periods so you can see the grand total of interest and the payoff date if you provide a start date. This is distinct from a regular loan or mortgage calculator, which assumes you pay principal from day one. It is a planning estimate for education only, not financial advice.
Frequently asked questions
What is an interest-only loan?
It is a loan where, for an initial period, you pay only the interest each month and the principal stays the same. After that period ends, the loan converts to a standard amortizing loan and your payment rises to cover both principal and interest over the remaining term. HELOCs, bridge loans, and some commercial mortgages work this way.
How is the interest-only payment calculated?
The monthly interest-only payment is the loan principal multiplied by the monthly interest rate (the annual rate divided by 12). Because none of it goes to principal, the balance does not change during this period, and the total interest is simply that monthly payment times the number of months.
Why does the payment jump after the interest-only period?
Once amortization begins, each payment must cover that month's interest plus enough principal to pay off the entire balance within the shorter remaining term. With fewer years left, the principal portion is larger, so the payment is higher than the interest-only payment was.
Is an interest-only loan a good idea?
It lowers your payment in the short term but costs more total interest, and you build no equity during the interest-only period. It can make sense for short-term financing, investors, or borrowers expecting higher income later, but it carries more risk. This tool is an estimate, not a recommendation.
