Ask a client whether they want a fixed or a variable mortgage rate and most will answer with a forecast. They think the question is where are rates going? — and since nobody knows, the conversation stalls into vibes and headlines. The question a mortgage advisor should actually be putting to them is different and far more answerable: which risk can this household carry? A fixed rate has a known cost. A variable rate has an unknown one. Choosing between them is not a bet on the market; it is an inventory of the borrower's capacity to absorb a payment that moves. This guide sets out how the two products differ mechanically, what the discount on a variable rate is actually paying for, a worked break-even example you can reuse with clients, and the handful of client circumstances that genuinely change the answer.
A fixed rate is a contractual promise that the interest charged will not change for a defined period — commonly two, three, five or ten years, and in some markets the entire term. The payment is knowable to the cent from completion to the end of the fix. What most borrowers miss is that the fix almost never runs to the end of the loan. A five-year fix on a thirty-year mortgage is a five-year product wrapped around a twenty-five-year liability. At the end of it the loan reverts to the lender's follow-on rate unless the borrower acts.
A variable rate is anything that can move. Within that label sit two quite different animals. A tracker is mechanically bound to a published benchmark — a central bank policy rate or an interbank index — plus a margin, so it moves when and only when the benchmark moves, by exactly that amount. A standard variable or discretionary rate is set by the lender, which may reprice it for reasons of its own funding cost, competitive position or margin management. The first is transparent risk. The second is transparent risk plus counterparty discretion, and it is worth naming that distinction to a client rather than letting "variable" cover both.
What the variable discount is paying for
The starting rate on a variable product is usually lower, and it is tempting to read that as the lender being generous. It is not. Interest rate risk on a long-dated loan has to sit somewhere. When a lender fixes a rate, it hedges that exposure in the swap market and prices the hedge into the offer. The fixed rate you see is roughly the market's expected path of rates plus the cost of insuring against it. When a borrower takes a variable rate, they decline the insurance and keep the premium.
This reframing does most of the advisory work. It stops the client asking "will rates go up?" and starts them asking "if the payment rose by four hundred a month, what would I stop doing?" The fixed-rate premium is a price for a service — payment certainty — and like any insurance it is good value for those who cannot self-insure and poor value for those who can. A household with a thin surplus, no savings buffer and a loan sized at the lender's maximum cannot self-insure. A household with substantial headroom can.
A worked break-even example
Illustrative figures only — plug in your client's real ones, but the shape of the answer generalises. Take a €300,000 repayment mortgage over 25 years. The five-year fix is offered at 4.2%; the tracker starts at 3.6%.
Fixed at 4.2%: monthly payment ≈ €1,617 — unchanged for five years.
Variable at 3.6%: monthly payment ≈ €1,518 — today.
Initial saving: about €99 per month, or €1,188 a year.
Now suppose the benchmark rises 1.5 percentage points after two years, so the tracker resets to 5.1%. By then the borrower has banked roughly €2,376 of savings and paid the balance down to about €284,600. Repaying that balance over the remaining 276 months at 5.1% costs approximately €1,754 a month — some €137 above the fixed payment they declined. The accumulated saving is consumed in about 17 months, after which the variable borrower is behind and stays behind for as long as the rate holds.
Two things fall out of that arithmetic. First, the break-even is far shorter than clients expect: a modest rise, arriving even a couple of years in, wipes out a discount that felt substantial monthly. Second, the risk is asymmetric in a way the headline rates hide — the €99 saving is capped, while the €137 penalty is not. Rates could rise further. That asymmetry, not a forecast, is the argument a stretched borrower needs to hear. Run the same table at plus one, plus two and plus three points and the client will usually answer their own question.
The borrowing-power side effect nobody mentions
The choice does not only change the payment; in many markets it changes the size of the loan on offer. Lenders underwrite affordability at an assessment rate above the contract rate — see the mortgage stress test for how that buffer is constructed — and a number of lenders relax or remove the buffer on fixes of five years or longer, because the payment shock they are guarding against cannot occur inside the fixed window. The practical consequence is that the same client, same income, same deposit, can be offered a materially larger loan on a long fix than on a tracker. If a purchase is failing on affordability by a small margin, testing the long fix before you tell the client to lower their sights is simply good practice. The mechanics behind that sizing are covered in how lenders assess affordability.
Circumstances that genuinely change the answer
Most of the time the client's balance sheet decides, not the yield curve. A short expected holding period argues for variable, because early-repayment charges on a fix can dwarf the rate difference — although many lenders now let a fix be ported to a new property, which removes the objection. An imminent lump sum, an inheritance, a business sale or a bonus cycle argues for variable, since variable products are commonly penalty-free to overpay or exit. A borrower whose income is volatile — commission, self-employment, seasonal work — argues for fixed, because a variable payment stacked on a variable income compounds two risks that are uncorrelated with each other and unhelpfully correlated with a recession.
And then there is the argument clients make most often and should trust least: "I'll take the tracker and fix later if rates start rising." You cannot fix at yesterday's price. By the time a rise is obvious enough to act on, the fixed rates on offer have already repriced to reflect it — the swap market moved before the policy rate did. Switching remains possible and often costless, but the product you switch into is tomorrow's, not the one you passed up. Say that out loud early; it is the single most useful sentence in the conversation.
Where the property valuation fits
Rate strategy is only half the risk in a purchase. The other half is whether the price is right, because a loan sized against an inflated purchase price leaves no cushion if the lender's valuation disagrees, and no equity to remortgage against when the fix ends. An advisor who has checked the price against comparable sales before the offer is locked is advising on both halves. This is where Biedradar fits an advisor's or agent's workflow: enter an address, get comparable sales, a valuation range and market signals, and produce a branded property analysis report in minutes — evidence you can put in front of a client rather than an opinion you have to defend.
How to frame it for the client
Do not present fixed versus variable as a forecast to be won. Present two payments and one question. Payment A is fixed and known for five years. Payment B starts lower and could plausibly land anywhere in a range you have modelled at plus one, two and three percentage points. The question is: at the top of that range, does this household still function? If the answer is a comfortable yes, the discount is real money and the client can rationally take it. If the answer is hesitation, they have just discovered they were never choosing between two rates — they were choosing whether to buy insurance they cannot afford to skip.
Advisors who work this way tend to keep clients longer, because the conversation is falsifiable and honest rather than predictive. Pair it with a documented view of the property's value — a property analysis report the client can read and keep — and you have covered what they pay each month and what they own outright. Then diarise the reversion date. The most expensive mortgage most people ever hold is the one they forgot to leave.
Frequently asked questions
What is the difference between a fixed and a variable mortgage rate?
A fixed rate is contractually locked for an agreed period — two, five, ten years, sometimes the whole term — so the monthly payment cannot change during that window. A variable rate moves: either because it tracks a published benchmark such as a central bank policy rate or an interbank index, or because the lender may reset its own standard rate at will. Fixed buys certainty at a premium. Variable buys a lower starting payment and hands the borrower the repricing risk.
Is a fixed or variable mortgage cheaper?
Over the life of the loan, neither reliably wins. A variable rate is usually cheaper on day one, because the borrower is being paid to carry the interest-rate risk the lender would otherwise hedge. Whether that discount survives depends entirely on the path rates take. The honest answer to a client is that a fixed rate has a known cost and a variable rate has an unknown one, and the question is not which is cheaper but which unknown the household can absorb.
When does a variable rate make sense?
When the borrower has genuine capacity to absorb a higher payment, a short expected holding period, or a realistic prospect of repaying early. A household with meaningful surplus income, a large deposit, an imminent sale, or a lump sum arriving can rationally take the discount. So can a borrower facing large early-repayment charges on a fix they would likely break. It rarely suits a stretched first-time buyer whose budget was sized by the lender's maximum.
What happens when a fixed rate period ends?
The loan reverts to the lender's standard variable or follow-on rate, which is typically well above the rates available on new business. Borrowers who do nothing therefore experience an unadvertised payment rise. The remedy is to remortgage or product-switch before the reversion date — usually arrangeable three to six months ahead. Diarising that date at the point of completion is one of the highest-value things an advisor can do for a client's long-run cost.
Does choosing a fixed rate change how much you can borrow?
It can. Many lenders apply a smaller stress-test buffer — or none at all — to mortgages fixed for five years or longer, because the payment they are guarding against cannot arrive during that window. The same borrower with the same income can therefore be offered a larger loan on a long fix than on a variable rate or a two-year fix. It is worth testing before concluding a client cannot afford a particular home.
Can you switch from a variable rate to a fixed rate?
Usually yes, and often with no early-repayment charge, since variable products are commonly penalty-free to exit. The catch is that the fixed rate on offer when the borrower panics is the fixed rate the market has already repriced. By the time a rise is obvious enough to act on, the cheap fix has gone. That asymmetry — you can only switch at tomorrow's prices — is the argument against treating variable as a fix you can grab later.
