How to use this compare
Enter the loan amount, term, the fixed rate you're offered, the variable start rate, the rate cap, and how often the variable rate adjusts. The tool amortizes both loans in parallel and shows monthly payment, total interest, and total cost side by side. The variable-rate model assumes the rate steps up by half the cap each adjustment period until it hits the cap — treat that as a stress test, not a forecast of what will actually happen.
What your result means
If the variable path shows total cost more than $1,000 lower than fixed, the tool leans variable — but only because it assumes you'd sell or refinance before rates climb to the cap. If fixed wins by more than $1,000, the certainty is likely worth it, especially on longer horizons where rates have more time to rise. Within $1,000 either way, the decision is a genuine toss-up and should hinge on your risk tolerance and how long you realistically expect to keep the loan.
When to trust it
The comparison assumes rates drift up steadily to the cap, which understates the risk if rates spike faster and overstates it if rates stay flat or fall. The model also can't predict life events — selling the home, refinancing, or paying early all change the outcome. For a mortgage specifically, ask the lender about the actual index and margin on the ARM, the current rate environment, and the break-even year before committing. A fee-only financial advisor can pressure-test the decision against your full picture.
Frequently Asked Questions
When does a variable rate actually make sense?
Three situations: you expect to pay the loan off quickly (before rates can rise much), current fixed rates are unusually high and you can refinance later, or the variable rate's cap is low enough that the worst case is still affordable. Variable rates typically start cheaper — the question is whether you can absorb the payment if the rate climbs 2-3 points. If a rising payment would break your budget, take the fixed.
How much riskier is a variable rate, really?
It converts interest-rate risk from the lender to you. On a $300,000 balance, each 1% rate increase adds roughly $250/month — a 3-point climb means ~$750/month of extra payment you didn't plan for. Historically, borrowers with variable rates sometimes win for years — until a rate cycle turns and payments jump faster than incomes. The discount you get at signing is the compensation for carrying that risk.
Can I switch from variable to fixed later?
Usually yes — most variable-rate products (mortgage ARMs, HELOCs, many private student loans) allow converting or refinancing to fixed. The catch: you convert at whatever the fixed rate is then, not today's. If you're switching because rates already rose, you lock in the higher number and lose the original advantage. Decide based on your payment-at-worst-case tolerance now, not on the hope of a free switch later.