Fixed vs. Variable Mortgages: A First-Time Buyer Comparison

The first mortgage illustration that lands in your inbox is dense with numbers, but one decision sits underneath almost all of them: do you want your rate locked for a set period, or left to move with the market? Get it right and your monthly payment fades into the background. Get it wrong and you can spend years paying more than you needed to, or paying an exit fee to escape a deal that stopped fitting.

Here is how both types of mortgage work, what they cost in practice, and how to tell which one belongs on your first home.

How each type actually works

A fixed-rate mortgage sets your interest rate for a defined period, usually two, three, five or ten years. Your payment is identical every month for that term, regardless of what happens to interest rates generally. When the fixed period ends, you move onto the lender's standard variable rate unless you remortgage or switch to a new deal first.

A variable-rate mortgage can change at any time. There are three common versions: a tracker, which follows the Bank of England base rate plus a set margin; a discount rate, which is the lender's standard variable rate with a reduction applied for a set period; and the standard variable rate itself, which is usually the most expensive place to end up. Your payment can fall, but it can also climb, sometimes quickly.

Fixed rates: the case for and against

What works well

• Certainty. You know the exact figure leaving your account on the 1st of every month for years, which makes budgeting for everything else far easier.
• Protection. If rates rise sharply, you are insulated until the fix ends.
• Useful when money is tight. A first purchase tends to arrive alongside other costs, and a predictable payment helps.

Where it can sting

• You pay for the certainty. Fixed rates often start slightly above the cheapest trackers available at the same moment.
• If rates fall, you do not benefit. You watch other borrowers' payments drop while yours sits still.
• Early repayment charges. Nearly all fixed deals carry them during the fixed period, which matters if you want to move, sell or remortgage early.

Variable rates: the same picture in reverse

Advantages

• Lower entry cost. The starting rate is often cheaper than an equivalent fix, so your first payments are smaller.
• Immediate benefit if rates fall, with no need to do anything.
• Flexibility. Many trackers carry no early repayment charge, so you can overpay, move home or switch lender without a penalty.
• Genuinely useful if you plan to overpay aggressively or expect to move within a few years.

Risks

• Your payment can jump, and not by a trivial amount. Budgeting becomes a moving target.
• If rates rise early in the term, you feel it immediately, before your income has grown.
• There is no cap. Do not take one on the assumption that rates will behave.

Side by side: what it means for your payment

Take a hypothetical £180,000 repayment mortgage over 30 years. At 3.8%, the monthly payment is roughly £840. At 4.5% it is about £912. At 6% it climbs to around £1,080.

Read those numbers as a story. A tracker starting 0.7 percentage points below a fixed deal saves you perhaps £75 a month at the outset — a real amount over a year. But two base rate rises wipe that saving out and then some, and the gap between the cheapest and worst outcome in that example is roughly £240 a month. That is the trade: a smaller starting payment in exchange for carrying the risk of it growing.

Which one suits you?

A fixed rate usually fits if you...

• Are stretching your budget to buy and could not absorb a payment increase of £150 or more.
• Plan to stay in the property for at least as long as the fixed period.
• Value knowing the number in advance more than you value the chance of paying less.

A variable rate can fit if you...

• Have a comfortable buffer each month and could still pay if the rate rose by one or two percentage points.
• Intend to overpay steadily, and want a deal without an early repayment charge.
• Expect to move, sell or remortgage within a few years and want to keep your options open.

The middle path

You do not have to pick an extreme. A two- or three-year fix reduces the commitment, while a tracker with no early repayment charge gives you flexibility without a long lock-in. Some fixed deals allow overpayments of up to a set percentage of the balance each year — often around 10% — which covers more than most buyers need.

Compare costs, not just the headline rate

The rate on the illustration is rarely the whole story. Work through this list before you decide:

1. Arrangement or booking fee. Check whether it can be added to the loan, and remember that adding it means paying interest on it for decades.
2. Early repayment charge. How much is it, and how long does it run?
3. Overpayment allowance. A fixed deal with no flexibility on overpayments can cost you more in interest than a slightly higher rate that lets you chip away at the balance.
4. The follow-on rate. Ask what you will pay when the deal ends. It is the number most buyers forget to check.
5. Portability. If you might move, can you take the mortgage with you?

A practical way to decide

Start with the stress test. Take the variable rate you are being offered and add two percentage points. If that payment would put you under real pressure, the fixed deal is buying you something worth having. If it would be uncomfortable but manageable, and you would rather keep the flexibility, the variable route stays open.

Then ask how long you realistically expect to stay. First homes tend to be held for shorter periods than buyers expect, and an early repayment charge can quietly eat the savings from a long fix. Compare the total cost over the fixed period — rate plus fees — rather than the monthly figure alone. Finally, get the numbers from more than one lender, and consider speaking to a whole-of-market mortgage broker. Mortgage advice is regulated for a reason, and a broker can test your circumstances against deals you will never see advertised directly.

A decision you can live with

There is no universally correct answer, only the one that matches your tolerance for uncertainty. If a rate rise would keep you awake, take the fix and treat the slightly higher payment as the cost of sleeping well. If you have room to absorb a rise and value flexibility, a variable deal may serve you better while it lasts. Whichever you choose, diarise the date your deal ends, roughly six months ahead, so you can start shopping for the next one before you drift onto a standard variable rate.

Photo: Jakub Zerdzicki / Pexels