Mortgage Arm Calculator

A fixed-rate mortgage locks one payment for 30 years; an adjustable-rate mortgage (ARM) starts lower and then changes. The number that names it — 5/1, 7/1 — tells you the deal: the first figure is how many years the low 'teaser' rate is fixed, the second how often it adjusts after that. When the rate adjusts, the loan re-amortizes — the remaining balance is spread over the remaining term at the new rate — so a higher rate means a higher payment, often a sharply higher one. Where does the new rate come from? A published index (a market rate) plus a fixed margin the lender sets, together the 'fully-indexed rate.' Caps limit the damage: a typical 2/2/5 structure means the first adjustment can move the rate at most 2 points, each later one at most 2 points, and it can never rise more than 5 points above where it started. The appeal is real — for the intro years you pay less than a comparable fixed loan, sometimes much less. The risk is just as real: when the teaser ends, the payment can leap, and the early savings get eaten if you keep the loan long enough. That makes an ARM a bet — that you'll sell or refinance before the reset catches up, or that rates will fall instead of rise. The simulator races an ARM's monthly payment against the fixed loan you could take instead: a flat line for fixed, a teal staircase for the ARM that sits low through the teaser, then steps up at each reset. The crossover — where the ARM's running cost overtakes the fixed loan's — is the hidden break-even. The durable lesson: the rate on the billboard is the teaser, not the loan; an ARM only wins if you collect the discount and get out before the reset bites.

Free and interactive — no sign-up, nothing to install. Read the full lesson for the plain-language explanation.