If you only learn one thing about payment fees, make it this: the headline rate lies, and the effective rate tells the truth.
What is an effective rate?
Your effective rate is simply:
| Term | Meaning |
|---|---|
| Total fees | Everything the processor charged you in a period |
| Total volume | The card sales you ran in that period |
| Effective rate | Total fees / total volume x 100 |
It collapses the percentage rate, the fixed per-transaction fee, monthly fees and surcharges into a single percentage you can compare across processors.
The fixed fee is the hidden cost
Most flat-rate processors charge a percentage + a fixed fee, e.g. Stripe and Square at 2.9% + $0.30. The percentage scales with sale size, but the fixed $0.30 does not:
| Average sale | 2.9% part | + $0.30 fixed | Effective rate |
|---|---|---|---|
| $5 | $0.145 | $0.30 | ~8.9% |
| $10 | $0.29 | $0.30 | ~5.9% |
| $50 | $1.45 | $0.30 | ~3.5% |
| $200 | $5.80 | $0.30 | ~3.05% |
A coffee shop running $5 tickets pays nearly triple the headline percentage once you include the fixed fee. That is why low-ticket merchants must care about the fixed fee, not the percentage.
How to use this
- Low average ticket? Favor a small fixed fee. Helcim (interchange + 0.40% + $0.08) and bank debit beat 2.9% + $0.30 on small sales.
- High average ticket? Favor a low percentage. Interchange-plus and subscription processors win because the percentage markup is tiny.
- Always model your real numbers in the effective-rate calculator — it blends volume, ticket size and international mix and ranks every processor.
See also: Stripe vs PayPal and the cheapest processor for small business.