Every bank that participates in CASS, the UK's account-switching infrastructure, has its quarterly gains and losses published by Pay.UK. Most of that reporting gets read quarter by quarter, in isolation. Pull five years of monthly volume data and five quarters of bank-level results together, though, and a different story shows up: switching in the UK isn't a steady drip, it's a seasonal cycle, and only some banks appear to be building their acquisition strategy around it.
The market has a heartbeat
Personal current account switching follows the same shape every single year since CASS launched: a sharp dip every May, then a steady climb through summer and autumn to a peak in October or November, before falling back in December. This holds in 2021, in 2022, in the record-breaking year of 2023, and again in 2024 and 2025. Whatever is driving the May trough, likely a post-tax-year-end lull combined with reduced switching incentive activity, it is remarkably consistent.
2023 remains the high-water mark, peaking at 160,523 personal switches in November, nearly 2.5x the May trough of the same year. 2025 and early 2026 track below the 2023 peak but well above the 2021–2022 baseline, suggesting the market has settled into a higher steady-state rather than continuing to climb indefinitely.
One bank dominates, and it isn't close
Across the four quarters of 2025, Nationwide posted a net gain of 215,902 customers, more than five times the next-best performer (Monzo, at 36,104). Every other bank in the table is either marginal or negative on a 12-month view. Halifax (-73,429) and Santander (-65,253) are the clearest losers, with J.P Morgan Chase and Barclays also posting significant net outflows over the full year.
The quarter-by-quarter view changes the story
The annual rollup hides a sharper pattern that only becomes visible when results are not flattened. Two things stand out:
Nationwide's strongest quarter is the market's strongest quarter. Its Q4 2025 net gain (+64,527) lands in exactly the same period as the year's seasonal peak (October–November). That correlation, present across every quarter of the year, suggests Nationwide isn't just absorbing a fixed share of whatever volume exists, it is actively timing its acquisition push to the moment the market is most active.
Barclays and Lloyds flip from losing to winning, in the same quarter, at the same time as the seasonal peak. Both banks ran net losses or were flat for the first three quarters of 2025, then swung sharply positive in Q4 (+18,534 and +12,073 respectively). That kind of simultaneous, sharp reversal across two unrelated banks in the same quarter looks far more like a coordinated cash-incentive cycle, common in UK retail banking around October–November ahead of year-end budget deployment, than an organic shift in customer sentiment.
Monzo is flat, on purpose or not. Across all four quarters, Monzo's net gain barely moves, sitting between +8,246 and +9,934 regardless of whether the broader market is at its May trough or its autumn peak. Every other bank in this analysis shows some seasonal sensitivity; Monzo shows none. That's consistent with a growth strategy built on always-on digital acquisition rather than reactive incentive campaigns, account opening at Monzo doesn't appear to respond to the same seasonal triggers that move the rest of the market.
Halifax and Santander lose the most exactly when competition is fiercest. Both banks' worst quarter for losses is Q4, the same quarter when Nationwide, Barclays and Lloyds are all running their strongest campaigns. Their retention problem compounds precisely when the competitive environment is most hostile.
Bank bars positioned at quarter midpoint month. Q1 2026 bank-level data not yet published (three months in arrears).
So what?
For a challenger or growth-stage bank thinking about its own acquisition strategy, this data suggests two genuinely different playbooks exist side by side in the same market. One is seasonal and incentive-led: ride the autumn peak hard, accept quieter months, and compete directly for switchers using cash bonuses timed to the cycle. The other is steady-state and digital: build acquisition that doesn't depend on the CASS cycle at all, and treat full switches as a separate, slower-moving objective from raw account growth.
Nationwide is clearly running the first playbook better than anyone else in the market. Monzo appears to be running the second, deliberately or as a byproduct of how its growth has scaled. Neither is wrong, but they are not the same strategy, and conflating "accounts opened" with "switches won" risks misreading which playbook is actually working.
Data source: Pay.UK Current Account Switch Service monthly and quarterly dashboards, January 2021–May 2026 (monthly volumes) and Q4 2024–Q4 2025 (bank-level gains/losses, personal accounts only). Bank-level data is published three months in arrears; Q1 2026 bank-level results were not yet available at time of writing.