Reviewed 30 September 2026 · quarterly cycle
Why do two identical parcels cost different amounts?
Surcharge periods, band boundaries and divisor differences. All three change the bill without changing the parcel.
The evidence
Surcharges are published but applied by period, which means fuel and peak components attach to calendar windows rather than to parcels. Two identical shipments a month apart can therefore differ with no change to the goods or the destination. This is the mechanism behind the most common experience in this category, and it is not evidence that anything went wrong.
Band pricing produces the second difference. Where a line prices by weight band rather than linearly, a parcel at the lower edge of a band and one at the upper edge are priced as the same product. A small change in contents can cross a boundary and change the tier, which makes marginal cost different from average cost.
The third difference is the divisor, which is published per service rather than per carrier. Two services under one brand can use different divisors, which means the same box bills differently depending on which service was booked. In our Q1 review we corrected our own recording from per-carrier to per-service because of this, and the correction is recorded in the snapshot series.
When this does not apply
Where the warehouse measurement differs, the bill differs for a reason that is about the parcel rather than about the line. Comparing the measured dimensions against the dimensions you supplied is the first check when two supposedly identical parcels cost differently, because a repack can change the volume without changing the contents.