What Is an Interest Rate Buy-Down ROI Calculator?

A rate buy-down is a trade: you hand the lender cash at closing, and in return your interest rate falls for the life of the loan. The cash takes the form of discount points, where one point equals one percent of the loan amount, and the reward is a smaller monthly payment and less interest over the term. The question the trade really asks is whether the money you hand over earns back more than it costs, and this calculator answers that by computing the break-even period, the lifetime saving, and the return on the cash you commit.

The decision is not automatic in either direction. A buy-down that pays for itself in three years is attractive to a borrower who intends to stay put, while the same buy-down is poor value to someone who expects to refinance or sell within two years. Turning the choice into a rate of return, and comparing that return against the alternatives for your cash, is the point of the calculation.

How It Works

The calculator computes two loan schedules from the standard amortisation formula PMT = P x r / (1 - (1 + r)^-n): one at your base rate and one at the bought-down rate, using the same principal and term. The monthly saving is the difference between the two payments, and the upfront cost is the points percentage applied to the loan amount plus any additional costs you entered. Dividing the upfront cost by the monthly saving gives the break-even period in months.

Lifetime saving is the monthly saving multiplied by the number of payments, minus the upfront cost, so it represents the net benefit if you keep the loan to maturity. ROI expresses that net benefit as a percentage of the upfront cost, which is the effective return on the cash you tied up in points. Total interest under each scenario is also reported so the interest reduction is visible directly.

Understanding Your Results

The primary card shows the break-even period, with the monthly saving, upfront cost, and lifetime saving beside it. If break-even lands inside the time you expect to hold the loan, the buy-down is working in your favour; if it lands outside, you would sell or refinance before recovering the cost. The breakdown table compares payment and total interest under both rates, and the difference row shows the interest reduction the points purchase.

Summary Statistics adds both payments, the total upfront cost, the break-even month, the net lifetime saving, and the ROI on the points. Remember that the return is realised gradually and only if you hold the loan, that points may or may not be tax deductible depending on how you itemise and how the funds are used, and that a temporary buy-down reverts after its introductory period, which changes the arithmetic completely. Treat the output as a planning estimate and confirm the exact point cost and rate reduction with your lender before deciding.