About the ARM Mortgage Calculator
An adjustable-rate mortgage (ARM) starts with a lower fixed rate for an initial period — like 5, 7, or 10 years — then adjusts. The initial savings can be real, but the payment can rise when the rate changes. This calculator shows your fixed initial payment and estimates the payment after adjustment so you can weigh the risk.
How it’s calculated
The initial payment uses the standard amortizing formula at the initial rate over the full term. After the fixed period, the remaining balance is re-amortized at the estimated adjusted rate over the remaining months to estimate the new payment.
Example calculation
A $320,000 5/1 ARM at 5.5% starts near $1,817/month. If the rate rises to 7.5% after five years, the payment on the remaining balance could climb to roughly $2,200/month.
Frequently asked questions
What does 5/1 ARM mean?
The rate is fixed for the first 5 years, then adjusts every 1 year after that. Other common ARMs are 7/1 and 10/1, with longer fixed periods.
How high can my payment go?
Real ARMs have periodic and lifetime rate caps that limit increases. This calculator estimates a single adjustment to the rate you enter; your actual loan's caps set the true ceiling.
Is an ARM a good idea?
It can be if you'll sell or refinance before the fixed period ends, or if you expect rates to fall. If you'll keep the loan long term, the payment risk after adjustment is the trade-off.
This calculator provides estimates for educational purposes and should not be considered financial, tax, or legal advice. Your actual figures may vary with lender terms, fees, and market conditions.