Choosing between a fixed-fee and percentage card machine plan
Card machine pricing usually comes in two flavours: a flat monthly fee that covers your processing, or a percentage of every transaction. The headline numbers look very different — but the right choice depends entirely on how your business actually trades.
Here's how to figure out which model leaves more money in your pocket.
Fixed-fee plans
You pay one predictable monthly amount — say £29 or £79 — and process up to a defined volume of card transactions at no extra cost. Anything above the cap is charged at a small per-transaction rate.
Pros: predictable budgeting, no nasty surprises in a busy month, simple statements. Cons: you pay the full fee even in a quiet month when you've barely used the terminal.
Percentage (interchange-plus) plans
You pay a small percentage of every transaction — typically 0.4%–1.6% depending on card type — plus a fixed pence-per-transaction authorisation fee. There's usually a small or zero monthly fee.
Pros: cost scales with revenue, so quiet months cost almost nothing. Cons: a runaway peak month produces a runaway bill, and the rate maths gets opaque fast once commercial and international cards enter the picture.
High volume, steady year-round → fixed-fee usually wins. Lower volume or highly seasonal → percentage usually wins.
Run the maths on your own numbers
- Pull your last 12 months of card turnover.
- Multiply your average monthly turnover by the quoted percentage rate.
- Add the per-transaction auth fee × your average monthly transaction count.
- Compare that figure to the fixed monthly plan that covers your volume.
- Repeat the maths against your busiest and quietest months — not just the average.
Don't forget the hidden lines
Both models can hide PCI fees, monthly minimums and chargeback charges. Always ask for an itemised quote, and run the comparison on your total effective rate — not the headline number.
"The cheapest plan on paper is rarely the cheapest plan once your actual mix of cards, months and ticket sizes is in the spreadsheet."
- Fixed-fee suits steady, high-volume businesses.
- Percentage suits seasonal or lower-volume traders.
- Always model both against your real 12-month data.
- Stress-test on your worst month, not your average.
- Itemise every fee — that's where the real comparison happens.
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