Fixed vs variable rate: who carries what

The difference is not the number on the offer. It is who is exposed if rates move, and in which direction.

A fixed rate hands the risk of a rise to the lender for the length of the fixed period. If the benchmark climbs, the lender keeps receiving the contracted rate while funding the loan at a higher cost. Your payment does not move.

What a fixed rate does not do is make you indifferent to rates. If the benchmark falls, you keep paying above what a new borrower is charged, and getting out of that can cost money. The lender took one direction and you kept the other. Fixing is a position, not the absence of one.

A variable rate leaves the rise with you and gives you the fall. The rate is written as a published index plus a margin the contract sets once, so the moving part is the index. In the United States that is commonly a Treasury-based series, SOFR, or the prime rate most cards are priced off. Index names are not permanent: LIBOR anchored a large share of the world's floating-rate contracts and then stopped being published, which is why loan documents now carry fallback language naming a replacement.

The premium a fixed rate carries is not simply a fee for holding risk. A fixed quote and a variable quote for the same borrower on the same day differ mostly because the market expects short rates to be somewhere other than where they are now, with a term premium on top and, where the borrower can repay early, the cost of that option as well. That is why the gap moves with the shape of the yield curve rather than sitting at some constant charge, and why it can close or invert.

Deposits run on the same logic pointing the other way. A saver is hurt by falls rather than rises, so a variable savings account leaves the saver exposed while a fixed-term deposit, a certificate of deposit in the United States, moves that exposure onto the bank. Fixing always transfers rate risk to the institution. What changes is which direction of move hurts.

A variable rate with no ceiling is an open-ended commitment. Whether the contract bounds it is a matter of market and product, not a feature of variable rates as such.

In the United States an adjustable-rate mortgage usually carries three limits, printed in the documents as a short series of numbers. An initial cap limits the first adjustment when the opening fixed stretch ends. A periodic cap limits each adjustment after that. A lifetime cap sets a rate the loan can never pass, conventionally several percentage points above the opening rate. The figures differ by product and by lender, so they are a term to read rather than a standard to assume.

Elsewhere the assumption fails outright. UK tracker mortgages and euro-area loans priced off Euribor commonly carry no rate ceiling, and a borrower who has read a US explainer will look for a cap the contract does not contain. Find the ceiling in your own documents before relying on one.

A floor is the same idea pointing down: the rate will not drop below it however far the index falls. Floors protect the lender's margin, and they are why a variable loan sometimes stops following the index on the way down.

Where caps exist they turn an open-ended exposure into a bounded one. That is worth something, and less than it sounds. Price the payment at the lifetime cap and ask whether the budget absorbs it, because that is the payment the contract already permits. The loan payment calculator will give you both figures, and a debt-to-income ratio run at the capped payment says more than one run at today's.

One structure is worth naming even though it has become rare. A few products cap the payment rather than the rate: interest the payment does not cover is added to the principal, so the balance climbs while the payment sits still. Post-crisis US rules pushed that structure out of mainstream residential lending, but it still turns up in other products and other markets.

Four things decide this, and not one of them is a rate forecast.

How long you keep the debt. A fixed period earns its premium only across the time you actually hold the loan, so someone who expects to sell or refinance inside the opening fixed stretch of a hybrid loan is paying from day one for years they may not be there for. The counterweight is that plans are unreliable in exactly the way that matters: the sale that falls through leaves you holding a loan that is about to reprice.

How much headroom the budget has. If a rise to the cap, or beyond it where there is no cap, would push something else out of the month, the cheaper opening rate is not cheaper. It is a position you cannot hold.

How wide the gap is, and what paying it has been worth. The premium is a price like any other, and a fixed rate costing a fraction of a point is a different decision from one costing several. It is also a price paid every month rather than only in the states of the world where it pays off. A term premium is, by construction, compensation the party carrying the risk usually keeps, which is why over long stretches variable-rate borrowers have on average paid less than fixed-rate ones. Insurance that is never claimed is still insurance, and it is still a cost.

What changing your mind costs. Leaving a fixed rate early can carry a charge, and replacing any loan costs whatever arranging a new one costs, whichever way rates went. Under current US rules prepayment charges on residential mortgages are tightly restricted and absent from most of them; other products, and other countries, work differently, and UK fixed deals routinely carry early repayment charges that run for the length of the fixed term.

None of that resolves to a rule, because the two are not a safe option and a risky one. They are two ways of pricing the same loan. The question is which risk you would rather hold and what the market is charging you to hand it over.

Two offers can share a headline rate and still behave differently, because the rate is one term among several.

On a variable loan the margin is fixed for the life of the contract, the index is not, and the opening rate is often set independently of both. So the figure to compare is the fully indexed rate: today's index plus the margin, which is where the loan lands once any discount ends. Two lenders advertising the same opening rate on different margins arrive at different fully indexed rates, and the wider margin stays more expensive from then on.

Reset frequency does its own work. A loan that reprices once a year and one that reprices monthly answer the same move at different speeds, and the annual one can sit away from the market for months in either direction before it catches up.

An opening rate can also be temporary by design. A hybrid mortgage is fixed for an opening stretch and variable afterwards. An introductory card rate is a promotion with an end date already written into the agreement, not a fixed rate at all. Compare the fixed offer against what the variable one becomes, not against its first few statements.

Comparing the two on APR helps, and only partly. An APR on a variable loan has to assume something about a rate nobody knows, so it is a projection printed as though it were a fact. The fixed-rate version is firmer without being a plain statement of terms either, because it spreads fees across the full term and so flatters a loan you clear early. The APR against APY comparison sets out what that figure does and does not fold in.

And a fixed rate is not the same thing as a fixed payment. Where taxes and insurance are collected alongside the loan, which is the normal arrangement in the United States and not the norm everywhere, the total moves when they move.