Current Affairs · Refinance
Big 4 Back-Book Rates After the May 2026 Hike — How Much You're Overpaying
The RBA hiked +0.25% on Tuesday 6 May 2026. Westpac has now confirmed its variable home loan rates rise 0.25% from Friday 15 May 2026. The other Big 4 banks will follow within days. But here's what most homeowners don't realise — they were already paying about 2 percentage points more than new customers before the hike. Here's the math.
The TL;DR
- Westpac existing-customer Flexi First (Owner Occ, P&I): 7.93% → 8.18% p.a. from 15 May
- Westpac best new-customer rate (Flexi First Online Special): 5.84% p.a.
- Gap = about 2.3 percentage points — pure loyalty tax
- On a $700K loan, that's about $1,150/month or $13,800/year in extra interest
- Interest-Only customers face higher rates again: 8.77% – 9.42% p.a. from 15 May
What is a "back-book" rate?
Banks divide their mortgage customers into two pools. The front book is new customers — the people the bank is actively trying to win. They get the sharp advertised rates, cashback offers, fee waivers, and hand-holding through the process.
Then there's the back book — existing customers who are already locked in. These borrowers receive less favourable pricing, smaller rate cuts when the RBA cuts, faster rate hikes when the RBA hikes, and almost zero promotional incentives. The bank doesn't have to compete for them — they're already there.
The ACCC has documented this two-speed pricing pattern across all Big 4 banks since their 2020 Home Loan Price Inquiry. The findings haven't changed: existing customers pay materially more than new customers for the exact same product.
The Westpac numbers, in plain English
Westpac confirmed on its official interest rates page that variable home loan rates rise 0.25% from Friday 15 May 2026. Here are the rates for the two most common products — split clearly between Principal & Interest (what most owner-occupiers have) and Interest Only.
Rates below assume LVR 70–80% and exclude Premier Advantage Package or LVR discounts. Source: Westpac May 2026 rate change notice.
Owner-occupier rates
| Product | Customer type | Current | From 15 May |
|---|---|---|---|
| Flexi First Online Special (P&I) | New customer | 5.84% | 5.84%* |
| Flexi First Option (P&I) | Existing | 7.93% | 8.18% |
| Rocket Repay (P&I) | Existing | 8.58% | 8.83% |
| Flexi First Option (Interest Only) | Existing | 8.52% | 8.77% |
| Rocket Repay (Interest Only) | Existing | 9.17% | 9.42% |
*Westpac's promotional new-customer rate is reviewed periodically and may move independently of back-book rate changes.
For a typical owner-occupier on Principal & Interest — the most common loan type — the gap is between 8.18% (back book) and 5.84% (front book). That's a 2.34 percentage-point gap, paid month after month, year after year, for the same loan product. Interest-Only customers face an even wider gap.
The other Big 4 — CBA, ANZ, NAB — follow the same pricing pattern. The exact numbers vary by ±0.2%, but the front-book vs back-book gap is structurally similar across all of them.
What this gap costs you each month
Three real Sydney loan sizes, comparing the post-15-May Flexi First back-book P&I rate (8.18%) against Westpac's best new-customer P&I rate (5.84%). Repayments are calculated over a 30-year term using the same method as ASIC's MoneySmart calculator.
| Loan size | Back-book (8.18%) | Refinance (5.84%) | Saving / month | Saving / year |
|---|---|---|---|---|
| $500,000 | $3,734/mo | $2,946/mo | $788 | $9,456 |
| $700,000 | $5,227/mo | $4,124/mo | $1,103 | $13,236 |
| $1,000,000 | $7,468/mo | $5,891/mo | $1,577 | $18,924 |
That's the loyalty tax for a typical owner-occupier on Principal & Interest. For most Sydney homeowners with mortgages between $500K and $1M who haven't reviewed their loan in 2+ years, real savings will be somewhere in this range. Interest-Only borrowers see even larger savings because their back-book rates are higher again (8.77–9.42% from 15 May).
The 15 May hike makes the maths worse, not better
Westpac confirmed the 0.25% rate increase will apply to all existing variable home loan products from Friday 15 May 2026. New-customer promotional rates often get smaller increases — sometimes none at all — because banks compete harder for new applications. Expect CBA, ANZ and NAB to make near-identical announcements within days.
Why don't existing customers just call and ask for a discount?
Some do, and it can work. A direct call to your bank's retention team can sometimes secure a 0.3–0.5% rate cut if you threaten to leave. But it almost never closes the full gap. The retention team's brief is to keep you below the cost-of-acquisition for a new customer — that's typically 1.0–1.5% above what new customers pay, not at parity.
The only way to actually access front-book pricing is to become a front-book customer somewhere else. That means refinancing.
What the refinance actually involves
This is where most borrowers procrastinate. The perception is that refinancing is a months-long ordeal. The reality, for a clean PAYG owner-occupier on a variable rate, is much simpler:
- Day 1–3: Rate review with broker. We compare your current rate against our wider lender panel, identify 2–3 strong options, model the savings.
- Day 4–10: Application submitted to chosen lender. Conditional approval typically returned within 48–72 hours.
- Day 11–25: Property valuation, formal approval, loan documents issued. You sign and return.
- Day 25–40: Settlement. Old loan discharged, new loan funded. From this date you're on the new rate.
Total time: 4–6 weeks from first conversation to first reduced repayment. Cost: typically $400–$900 in fees, often offset by a refinance cashback of $2,000–$4,000 from the new lender. Our refinance team handles the paperwork end-to-end.
When refinancing isn't the right move
Three situations where the maths doesn't work:
- You're locked into a fixed rate with break-fee exposure that exceeds your potential savings. Wait until the fixed term ends, then refinance.
- Your equity has dropped below 80% LVR (e.g. you bought near peak and the property has softened). Refinancing would trigger LMI, which can wipe out the savings.
- You're planning to sell within 12 months. The refinance break-even period is usually 3–6 months; if you're selling sooner, the cost of switching may exceed the saving.
Outside these scenarios, the May 2026 environment makes refinancing a higher-priority decision than it was 6 months ago. The back-book gap was already costing you. The hike just made it cost more.
After the May 2026 hike
Free 20-minute rate review — find out exactly what you're paying vs what you could pay
We'll compare your current rate against our wider lender panel and tell you within 24 hours whether refinancing makes sense. If it doesn't, we say so and you stay put. No fees, no obligation, no credit check at this stage.
Get My Free Rate Review →Frequently Asked Questions
A back-book rate is the higher variable rate that lenders charge existing customers compared to the discounted rates offered to new customers. The gap is the loyalty tax — it can exceed 2 percentage points for borrowers who haven't reviewed their loan in 2+ years.
Westpac's published existing-customer reference variable rates currently range from 7.93% to 9.17% p.a. Their best new-customer rate is 5.84%. On a $700,000 loan, the gap between 8.5% and 5.84% is approximately $18,500 per year in interest. Even moderate refinances typically save $7,000–$15,000 per year.
It's called the loyalty tax. Banks know that most existing customers don't review their rate annually, so they raise back-book rates faster than new-customer rates and pocket the margin. The ACCC has documented this pricing pattern across all Big 4 banks since 2020.
Yes. Lenders typically pass RBA rises through to back-book rates within 2-4 weeks. New-customer rates often get smaller increases (or none, on promotional products) because banks compete harder for new business. The May 6 hike will widen the back-book gap further over the next month.
For most variable-rate loans: $300–$600 discharge fee from your current lender, $100–$300 government fees, and $0–$600 establishment fee with your new lender. Many lenders are offering $2,000–$4,000 refinance cashbacks that more than cover these costs. Total break-even on a typical refinance is 3–6 months of saved interest.
Pre-approval typically 48–72 hours. Full settlement and discharge from old lender usually 4–6 weeks. You stay with your old lender (paying their back-book rate) until settlement completes. Starting now means new rate locked in by mid-June.
Stop overpaying — speak to a Mortgagefy refinance broker
Free rate review across our wider lender panel. We tell you exactly what's achievable in the post-hike market and whether refinancing now saves you money. No obligation, no broker fees.
Related guides
General information only. The information in this article is general in nature and does not constitute personal financial, taxation, or credit advice. RBA cash rate, lender rate, and bank pricing figures are current as of 10 May 2026 and subject to change. Repayment examples are illustrative and assume principal-and-interest payments over a 30-year term. Mortgagefy is an authorised credit representative under Australian Credit Licence 348324. Before acting on any information, consider whether it is appropriate to your personal circumstances and seek independent financial or credit advice. Sources: Reserve Bank of Australia, Westpac published rate schedule, ACCC Home Loan Price Inquiry — May 2026.