UK CPI on GBPJPY: 42 of 47 small-miss prints sent GBPJPY down, and the whole 5-bucket walk is cleaner than on GBPUSD
196 non-contaminated UK CPI (y/y) releases on GBPJPY, 15-minute window, split into five surprise buckets. Medians walk −20.9 / −22.2 / +2.6 / +9.75 / +11.45 pips big_miss → big_beat. Up-rate walks 31 / 11 / 54 / 69 / 81 percent, monotonic through all five buckets. 42 of 47 small-miss prints sent GBPJPY down; 13 of 16 big-beat prints sent it up.
Six days ago I ran the same analysis on UK CPI on GBPUSD. The 15-minute shape was the same: clean monotonic walk, beat-side big_beat 81% up, miss-side unanimity 13% at small_miss. GBPJPY gives you the same signs with ~35% bigger typical moves at the tails, and one extra pip of miss-side unanimity — 42 of 47 vs 41 of 47.

The 15-minute bucket table
| Bucket | n | 15m median | p25 | p75 | Pct up (15m) |
|---|---|---|---|---|---|
| big_miss | 13 | −20.90 | −38.40 | +1.60 | 31% |
| small_miss | 47 | −22.20 | −43.40 | −8.15 | 11% |
| in_line | 68 | +2.60 | −8.18 | +13.62 | 54% |
| small_beat | 52 | +9.75 | −1.53 | +24.05 | 69% |
| big_beat | 16 | +11.45 | +5.42 | +28.90 | 81% |
Read the pct-up column: 31 / 11 / 54 / 69 / 81— monotonic through all five buckets, with the small-miss bucket the cleanest of the lot. The p25 column runs deeply negative on both miss buckets (p25 = −43.4p at small_miss), so the direction isn’t being carried by a single outlier print.
The 5 small-miss prints that DIDN’T send GBPJPY down
Only five prints out of 47 broke the pattern. All five are borderline small-miss surprises (surprise_z between −0.67 and −1.50), and each corresponds to a day where broader risk sentiment overwhelmed the sterling-negative signal:
2014-12-16 1.0 vs 1.2 fc z=-1.34 +37.10p 2016-03-22 0.3 vs 0.4 fc z=-1.50 +44.40p 2018-11-14 2.4 vs 2.5 fc z=-0.67 +5.70p 2019-11-13 1.5 vs 1.6 fc z=-1.04 +7.50p 2025-04-16 2.6 vs 2.7 fc z=-0.73 +6.10p
The two largest exceptions (2014-12-16 and 2016-03-22) both landed in windows where the JPY leg dominated: December 2014 was mid-way through the BoJ’s QQE expansion phase (JPY pushed weaker against everything on the day regardless of UK data); March 2016 was the immediate aftermath of the Brexit-referendum announcement window when sterling was so noisy that a 0.1-point CPI miss was overwhelmed by cross-cutting political flow. The three smallest exceptions are near the boundary of the small_miss bucket (surprise_z between −0.67 and −1.04) — barely surprises at all.
Same-sign moves against GBPUSD
Across all 196 shared UK CPI releases, GBPJPY and GBPUSD moved the same direction on 176 of them — 89.8%same-sign. That’s the sterling leg dominating both crosses. The 20 divergent prints are the ones where the USD or JPY leg contributed an offsetting move — most commonly on days with a US CPI, ISM, or NFP release also on the calendar (contamination is filtered at the API level for the immediate 15-minute window, but longer-horizon macro sentiment still bleeds into the tape).
The 35% bigger typical move on GBPJPY comes from the JPY leg amplifying rather than offsetting: a UK CPI miss weakens sterling against USD (one push), and typically the same environment sees a modest JPY safe-haven bid (a second push in the same direction). Two forces of the same sign on GBPJPY versus one force on GBPUSD explains most of the size differential. This is a general property of JPY crosses, not something specific to UK CPI — see the earlier two-employment-reports post for the same amplification structure on CAD data through USDCAD.
What this doesn’t say
Tail buckets are small. big_miss n=13 and big_beat n=16. Per Stats for Traders #3, the distribution-free 95% CI on up-rate at n=13 with 4 successes spans roughly [10%, 61%] — the observed 30.77% is real evidence but the interval is wide. Treat the DIRECTION as trustworthy; the specific magnitude of the observed rate carries more uncertainty. The small_miss bucket at n=47 is where the strongest headline finding lives (42 of 47 down = 10.64% up).
The edge decays past the first hour. The gbpusd-uk-cpi-fades post already made the case for the USD cross; the same fade is visible on GBPJPY. Big_beat at 1h is still +10.55p (81% up), but by EOD it turns choppy: +8.60pmedian with pct-up dropping to 62%. Anyone trading past the first hour should carry a wider stop and expect noisier realised P&L.
UK CPI is not the only sterling-CPI signal. UK Core CPI y/y publishes at the same 06:00 or 09:30 UTC release window as headline CPI, and the two are always released together. This post uses the headline y/y series; the core version is a separate event in the tool but the bucket samples overlap heavily by construction.
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