Two pricing models dominate merchant accounts. Neither is automatically better — the break-even depends on your volume and your average ticket. Here's the honest math.
Flat rate (aggregators like Square/Stripe at their published rates): one percentage + a fixed per-transaction fee, same for nearly every card. Simple, predictable, instant to start. Interchange-plus: the wholesale interchange cost (set by the card networks, identical for everyone) plus a disclosed markup — a percentage and/or per-item fee set by your processor. Transparent, but the quote quality varies: the markup is the only negotiable part, and junk fees can hide next to it.
Assumptions, stated so you can redo this with your own numbers: $25,000/mo card volume; flat rate at a published 2.6% + 15¢; interchange-plus at an illustrative wholesale average of 1.80% + markup of 0.30% + 10¢.
Patterns to take away: the per-transaction fee punishes small tickets under both models; monthly account fees punish small volume under interchange-plus; and at steady five-figure volume, interchange-plus usually wins if the markup is honest and the fee schedule is clean.
Very low or seasonal volume; you value zero setup friction; your tickets are large; or your current alternative quote is loaded with junk fees that erase the theoretical edge.
Calculate my current effective rate Get the free audit
All figures in the worked example are illustrative assumptions, not quotes. Published flat rates are as published by the processors and change over time — see our disclaimer.