Payment processors compared
Every processor quotes a percentage plus a fixed fee. That structure means there is no cheapest processor in general — only a cheapest processor at your average order value.
The fixed fee is the whole story on small orders
A quoted "2.9% + $0.30" is not a 2.9% cost:
| Order | Percentage part | Fixed part | Total | Effective rate |
|---|---|---|---|---|
| $5 | $0.15 | $0.30 | $0.45 | 9.0% |
| $12 | $0.35 | $0.30 | $0.65 | 5.4% |
| $35 | $1.02 | $0.30 | $1.32 | 3.8% |
| $100 | $2.90 | $0.30 | $3.20 | 3.2% |
| $250 | $7.25 | $0.30 | $7.55 | 3.0% |
On a $5 order the "2.9%" processor costs 9%. Nothing is hidden — it is arithmetic almost nobody performs, which is why products under about $10 so often lose money in ways their sellers cannot locate.
Which structure wins depends on your order size
Compare two shapes — one with a low percentage and high fixed fee, one the reverse:
| Order | 2.4% + $0.45 | 3.4% + $0.10 | Cheaper |
|---|---|---|---|
| $8 | $0.64 (8.0%) | $0.37 (4.6%) | Low fixed |
| $20 | $0.93 (4.7%) | $0.78 (3.9%) | Low fixed |
| $35 | $1.29 (3.7%) | $1.29 (3.7%) | Identical |
| $80 | $2.37 (3.0%) | $2.82 (3.5%) | Low percentage |
| $200 | $5.25 (2.6%) | $6.90 (3.5%) | Low percentage |
They cross at $35. Below it the low-fixed processor wins; above it the low-percentage one does. If your average order is $12, optimise for the fixed fee and treat the percentage as secondary. At $150, the reverse. This is why a general "cheapest processor" recommendation is not answerable — and why the payment fee calculator compares three at once against your own order value.
The surcharges that are not in the quoted rate
Worth checking on a statement rather than a pricing page, because the pricing page summarises:
- Cross-border / international card surcharge — commonly added when the card was issued in a different country from your account.
- Currency conversion — applied when you are paid in a different currency from the one you charged, and usually a larger cost than sellers expect.
- Chargeback fees — a flat charge per disputed transaction, often regardless of whether you win.
- Monthly account or gateway fees — which, like a platform subscription, behave as a per-order cost that shrinks with volume.
- Payout fees — for moving money to your bank, particularly across currencies.
- Refund handling — many processors retain the fixed portion of the fee on a refunded transaction. On low-value orders with a high return rate this is material; it is an input in the return cost calculator.
The bigger lever is order value, not processor choice
Switching processor to save half a point is real but small and takes work. Raising your average order value moves every order down the effective-rate table and improves shipping economics at the same time. A free-shipping threshold or a bundle generally beats a payment renegotiation, and you control it entirely.