Fixed vs Variable Rates

Every loan rate quote is really two products. One sells certainty: a fixed rate that never moves, at a premium. The other sells a discount: a variable rate that starts lower and can go anywhere. Neither is universally better. The right choice depends almost entirely on one variable you control, your time horizon, and one you do not, where rates go next.

How Each One Works

A fixed rate loan locks its rate on day one. The payment calculated at closing is the payment in year 29. Rising market rates cannot touch you; falling rates pass you by unless you refinance.

A variable rate loan, called an adjustable rate mortgage or ARM in the US, starts with a fixed introductory period, then adjusts on a schedule. The new rate is a public market index plus a fixed margin set in your contract. A 5/1 ARM is fixed for five years, then adjusts annually. Caps limit each move: a common 2/2/5 structure allows at most 2 points at the first adjustment, 2 points per adjustment after, and 5 points total over the loan's life.

The Numbers: $400,000, Fixed vs 5/1 ARM

Suppose the fixed offer is 6.5% and the ARM intro rate is 5.75%, a typical sort of gap. On a $400,000 loan over 30 years:

• Fixed payment: $2,528 per month, forever.
• ARM intro payment: $2,334 per month, a saving of $194 per month, about $11,600 over the five year intro.
• If rates have risen and the ARM adjusts up by its full 2 point initial cap to 7.75%... the payment on the remaining balance of about $371,000 jumps to roughly $3,050, which is $716 above the intro payment and $522 above what the fixed loan would have been all along.

That is the whole trade in one example: a guaranteed $11,600 head start against a possible $500 plus monthly penalty for every year after, with the outcome decided by rate movements nobody can predict.

A Framework for Choosing

Match the fixed period to your horizon. If you are confident you will sell or refinance within the intro period, the ARM discount is money the fixed borrower simply leaves on the table. If you plan to hold the loan long past the intro period, you are speculating on rates with your housing payment.

Stress test the caps, not the intro rate. Before signing an ARM, compute the payment at the lifetime cap using our amortization calculator. If that payment would break your budget, the loan is a bet you cannot cover, whatever the odds.

Treat refinancing as an escape hatch, not a plan. The scenarios where your ARM adjusts sharply upward are the same scenarios where refinancing is expensive. Our refinance calculator shows the break even math when the moment comes, but qualification and closing costs are never guaranteed in advance.

Compare offers on APR, not the headline rate. Fees change the real cost of both loan types; the difference between APR and interest rate matters most exactly when two offers look close.

The Honest Summary

Fixed rates are insurance, and insurance costs money in the outcomes where you did not need it. Variable rates are a discount financed by risk you carry. Take the discount when your timeline genuinely fits inside the fixed period; pay for certainty when it does not. Deciding based on which intro payment looks nicer, without stress testing the adjusted payment, is how people end up in loans they cannot afford in year six.