Understanding SONIA, Swap Rates, and Global Market Impact
If you’ve been following recent news—particularly global events and economic uncertainty—you may be wondering:
Why are mortgage rates going up in the UK when the Bank of England base rate hasn’t changed?
The short answer:
Fixed mortgage rates are not directly linked to the base rate.
The longer answer is more interesting—and far more important if you’re considering a mortgage or remortgage.
The Key Drivers Behind Mortgage Rates
What is SONIA?
SONIA (Sterling Overnight Index Average) is:
- The average rate banks pay to borrow from each other overnight in the UK
- Based on real transactions, not estimates
- Published daily by the Bank of England
In simple terms:
SONIA reflects the real cost of money between banks right now
Why SONIA Matters
It helps to think of it like this:
- Bank of England Base Rate = the official rate set by policymakers
- SONIA = what money is actually costing in real markets
SONIA is the foundation for how financial markets price lending over time.
How SONIA Links to Your Mortgage
Here’s the chain that ultimately drives fixed mortgage pricing:
SONIA → Swap Rates → Fixed Mortgage Rates
Step 1: SONIA
Represents overnight borrowing costs between banks.
Step 2: Swap Rates
These reflect what markets expect interest rates to be in the future.
Step 3: Fixed Mortgage Rates
Lenders use swap rates to price mortgages:
Swap Rate + Lender Margin = Fixed Mortgage Rate
What Are Swap Rates (And Why They Matter)?
Swap rates are effectively:
The cost for lenders to “lock in” money over a set period (e.g. 2, 5, or 10 years)
Each mortgage term aligns with a swap rate:
- 2-year fixed → 2-year swap rate
- 5-year fixed → 5-year swap rate
Important:
Swap rates move daily based on market expectations—not just Bank of England decisions.
So Why Are Mortgage Rates Rising Right Now?
There isn’t one single cause—it’s a combination of factors.
1. Global Uncertainty
Events such as geopolitical tensions can lead to:
- Increased market volatility
- Higher perceived risk
- Greater demand for returns from investors
This can push swap rates higher.
2. Inflation Expectations
Global events can influence:
- Energy prices
- Supply chains
- Cost of goods
If markets expect inflation to rise or remain elevated:
They expect interest rates to stay higher for longer
Swap rates increase accordingly
3. Markets Move Ahead of Central Banks
A key point many borrowers miss:
- The Bank of England reacts to data
- The markets anticipate future changes
So even if the base rate remains unchanged:
- Expectations about future rate movements shift
- Swap rates adjust quickly
- Mortgage pricing follows
Why This Can Feel Confusing
It’s completely understandable that many borrowers think:
“But the base rate hasn’t changed…”
That’s true.
However:
Fixed mortgage rates are based on future expectations, not today’s base rate
A Simple Way to Explain It
You can think of it like this:
“A fixed-rate mortgage is the cost of securing money today for the future.”
Or even more simply:
“The base rate reflects today. Fixed mortgage rates reflect where the market thinks things are going.”
What This Means for Borrowers
1. Rates Can Rise Without Base Rate Changes
This is normal in modern financial markets.
2. Timing Matters
Mortgage pricing can change quickly, sometimes within days.
3. Individual Circumstances Matter
The most suitable option will depend on your personal situation, goals, and attitude to risk.
The Bigger Picture
Current mortgage pricing is being influenced by:
- Global economic uncertainty
- Inflation expectations
- Financial market sentiment
All of which feed into:
Higher swap rates
Changes in fixed mortgage pricing
Final Thoughts
If there’s one key takeaway:
Fixed mortgage rates are driven by market expectations of the future—not just the Bank of England base rate today.
And those expectations are shaped by both UK and global events.
👉 Book a chat here.
Important Information
- The information in this article is correct at the time of writing and is subject to change.
- This content is for general information purposes only and does not constitute financial advice.
- Mortgage rates and product availability will vary depending on individual circumstances.
- There may be a fee for mortgage advice. The precise amount will depend upon your circumstances.
Your home may be repossessed if you do not keep up repayments on your mortgage or any other debt secured on it.
GP Norgate Financial Solutions is a trading name of Easy Street Financial Services Limited, which is authorised and regulated by the Financial Conduct Authority. Easy Street Financial Services Limited is a company registered in England and Wales with company number 6430453. Registered Office: Basepoint, 377-399 London Road, Camberley, Surrey, GU15 3HL.