Why did my mortgage rate go up if the Bank of England hasn't changed the base rate?

Fixed mortgage rates aren't set directly by the Bank of England's base rate. They're priced off swap rates, which are what lenders pay in the wholesale money markets to fund a fixed-rate loan for two, five or ten years. Swap rates move on what investors expect interest rates to do in the future, not what the base rate is doing right now. This week the two-year SONIA swap rate rose from 3.978% to 4.177% and the five-year swap rose from 4.008% to 4.231%, driven by the escalating conflict in Iran and its knock-on effect on oil prices and inflation expectations (Moneyfacts, 21 July 2026). Bank Rate itself has been unchanged at 3.75% since 18 June 2026, with the next decision not due until 30 July. Lenders including Halifax, Barclays and HSBC responded by raising some fixed rates by as much as 0.2 percentage points. If you're partway through a mortgage application, check today's rate with your lender or broker rather than relying on a quote from even a few days ago.

What is a swap rate and how does it affect my mortgage?

A swap rate is the interest rate at which banks agree to exchange a variable payment for a fixed one over a set period, and it's the wholesale cost lenders use to price fixed-rate mortgages. When a lender offers you a five-year fixed rate, it's effectively borrowing at the five-year swap rate and adding its own margin and profit on top. Swap rates rise and fall on economic data, inflation expectations and global shocks well before the Bank of England ever changes the base rate, which is why fixed mortgage rates can move independently of, and sometimes in the opposite direction to, Bank Rate. This week's swap rate rise (Moneyfacts, 21 July 2026) is a textbook example: Bank Rate hasn't moved, but average two-year and five-year fixed mortgage rates have both risen to their highest one-day jump since April. If a lender's fixed rates are rising, assume more may follow within days rather than waiting to see if it settles down on its own.

Can my mortgage offer change after I've applied?

Once a lender has issued a formal mortgage offer, the rate on that specific offer is normally locked for its validity period, typically three to six months depending on the lender. What can change is any rate you haven't yet locked in: an agreement in principle, a rate you've seen advertised, or a product you were planning to apply for but haven't submitted. If you're still shopping around or your current rate reservation hasn't converted into a formal offer, this week's rate rises could reach you before completion. The safest move if you're close to applying is to ask your broker or lender whether you can reserve or lock a rate now, since most lenders let you do this before your mortgage offer is formally issued, sometimes for a small fee that is refunded if the rate falls before completion. Don't assume the rate you were quoted last week is still available today.

Should I lock in a mortgage rate now or wait?

If you have a completion date within the next few months and a rate you're happy with is available today, the maths generally favours locking it in rather than gambling on a fall. Average two-year and five-year fixed rates have just posted their sharpest daily rise since April (Moneyfacts, 21 July 2026), and geopolitical-driven rate moves like this one can persist for weeks if the underlying situation doesn't resolve quickly. Waiting to see if rates ease back down means accepting the risk that they instead climb further, and most lenders let you switch to a cheaper rate before completion if one becomes available, at little or no cost. If your fixed rate deal isn't ending for six months or more, there's less urgency, but anyone within striking distance of applying should get a rate reserved this week rather than next.

Mortgage rates jumped 0.2 points this week: here's why

You got your agreement in principle a few weeks ago. The rate looked fine, the sums worked, and you told yourself the hard part was finding a place, not paying for it. Then this week your broker mentions, almost in passing, that the rate you were counting on isn't guaranteed any more. The Bank of England hasn't done anything. Nobody announced a rate rise. And yet your mortgage just got more expensive.

Here's the number behind it: average two-year and five-year fixed mortgage rates both rose sharply on Tuesday, the biggest one-day jump for either product since 2 April, with several major lenders including Halifax, Barclays and HSBC increasing pricing by as much as 0.2 percentage points (Moneyfacts, 21 July 2026). Bank Rate is unchanged at 3.75% and won't be reviewed again until 30 July. What moved instead is something most buyers have never heard of: the swap rate.

What actually happened this week

The trigger is the escalating conflict in Iran. As the situation has worsened, financial markets have pushed up their expectations for inflation and future interest rates, and that has fed straight through into swap rates, the wholesale cost lenders pay to fund fixed-rate mortgages. The two-year SONIA swap rate has climbed from 3.978% a month ago to 4.177% today; the five-year swap has gone from 4.008% to 4.231% (Moneyfacts, 21 July 2026). Lenders reprice their mortgage ranges when their own funding costs move, and this week enough of them moved at once to push the market average up in a single day.

The mechanism behind that's worth understanding even in outline. Geopolitical instability in an oil-producing region tends to push up oil prices, and higher oil prices feed into inflation forecasts. When markets expect inflation to run hotter for longer, they also expect the Bank of England to need to keep interest rates higher for longer to bring it back under control. That expectation shows up first in swap rates, days or weeks before it could ever show up in an actual Bank Rate decision, because swap markets trade every day while the Monetary Policy Committee only meets eight times a year. It's not the first time this exact mechanism has moved rates this year, and it won't be the last.

To put that in cash terms: on an illustrative £180,000 repayment mortgage over 25 years, a rise from 5.4% to 5.6% (broadly the scale of this week's move) adds around £21 a month to the payment, using the standard UK repayment mortgage formula. That's roughly £515 over a typical two-year fix, or £1,288 over five years, for exactly the same loan on exactly the same property.

So if you haven't locked a rate yet, that's not a rounding error, it's real money leaving your budget every month for the length of your fix.

Why your mortgage rate isn't tied to the Bank of England

This is the bit that catches people out. Base rate and mortgage rates are related, but they're not the same thing, and they don't move on the same schedule. Bank Rate is set eight times a year by the Monetary Policy Committee and reflects where the Bank thinks interest rates should be right now. Swap rates are set by financial markets every single trading day and reflect where investors think interest rates are heading over the next two, five or ten years, priced in advance of any actual Bank of England decision.

That's exactly why the site has spent the last fortnight covering mortgage rates falling, then this week covering them rising, without a single Bank Rate decision in between. Our mortgage price war coverage from earlier in July showed six lenders cutting rates in 24 hours on the back of falling swap rates. This week, the same mechanism has run in reverse. Bank Rate has sat at 3.75% throughout both moves.

That means watching only for the next Bank of England announcement will leave you blindsided; the rate that actually affects your monthly payment can move on any weekday, for reasons that have nothing to do with UK monetary policy.

What this means if you're mid-application

Not every mortgage in the pipeline is affected equally. Once a lender has issued a formal mortgage offer, that specific rate is normally locked for a set validity period, usually three to six months. What's exposed is anything before that stage: an agreement in principle, a rate you saw advertised last week, or a product you were planning to apply for but haven't submitted yet.

Some of the very cheapest deals on the market, like Danske Bank's 4.13% two-year fix and Halifax's 4.17% five-year fix at 60% loan-to-value, were still showing on best-buy tables as of 21 July (HomeOwners Alliance / Moneyfacts, 21 July 2026), so the sharpest end of the market hasn't necessarily disappeared. But best-buy tables can lag same-day repricing by a lender, so treat any quote as provisional until your broker confirms it's still live today. If you've been comparing options via our mortgage calculator, it's worth rerunning the numbers at this week's rates rather than the ones you checked a fortnight ago.

So if you're still shopping rather than holding a signed offer, the smart move is to ask your lender or broker to reserve a rate today, not to wait and see if things settle.

Does a tracker mortgage sidestep the problem?

A tracker mortgage moves directly with Bank Rate rather than with swap rates, so it would have been unaffected by this week's move entirely. That sounds like an easy way round the volatility, but it isn't a free lunch. Tracker rates are priced with Bank Rate still at 3.75% and the Bank's own chief economist on record saying rates may need to rise over the coming year, so you would be swapping one uncertainty (swap-rate-driven fixed pricing) for another (a possible base rate rise landing directly on your payment with no notice period at all). A fixed rate at least gives you a known payment for the length of the deal, which matters if your budget has little slack. A tracker only makes sense if you have room to absorb a payment rise and are actively betting that Bank Rate falls faster than fixed rates do over your chosen term.

So unless you can comfortably afford a higher payment if Bank Rate does rise on 30 July or later in the year, a fixed rate remains the safer default while swap rates stay this jumpy.

The maths, in one place:

Illustrative £180,000 repayment mortgage, 25-year term: at 5.4% the monthly payment is roughly £1,095; at 5.6% (a 0.2 percentage point rise, matching this week's reported lender increases) it rises to roughly £1,116, a difference of about £21 a month. Over a two-year fixed term that's approximately £515 in total; over a five-year fixed term it's approximately £1,288. Calculated using the standard UK repayment mortgage formula: payment = loan × (monthlyRate × (1 + monthlyRate)^n) / ((1 + monthlyRate)^n − 1), where monthlyRate is the annual rate divided by 12 and n is 300 months. Rates and swap-rate figures per Moneyfacts, 21 July 2026.

What this means for you

If you have a completion date within the next few months and a rate on the table today that fits your budget, the maths points toward locking it in now rather than betting on a fall. Geopolitical shocks like this one don't reliably reverse on a predictable timetable, and most lenders will let you switch down to a cheaper rate before completion if swap rates ease again, often at no cost. Waiting only exposes you to further rises with no guaranteed upside. If your current deal isn't ending for six months or more, there's less pressure to act this week, but anyone within striking distance of applying should get a rate reserved now. And if Stamp Duty is also part of your budgeting, it's worth reading our current Stamp Duty thresholds explainer alongside this one, since a rate rise and a tax bill land on the same completion day.