Flat-rate pricing charges one advertised percentage plus a fixed fee on every transaction, regardless of which card the customer uses. A debit card costing the processor 0.3% and a corporate card costing it 2.5% are billed to you identically. The processor absorbs the difference.
What you are actually buying
The processor is taking a position. Some months your customers use cheap debit cards and the processor profits handsomely; some months they use premium rewards cards and it loses money on those transactions. Across thousands of merchants, it wins on average — and you get a number you can put in a spreadsheet.
| Card used | Their cost | You pay | Their margin |
|---|---|---|---|
| Regulated debit | $0.41 | $3.20 | $2.79 |
| Standard credit | $1.75 | $3.20 | $1.45 |
| Premium rewards | $2.35 | $3.20 | $0.85 |
| Corporate card | $2.75 | $3.20 | $0.45 |
On debit the processor keeps most of the fee. On a corporate card it keeps very little. That spread is the insurance premium you are paying, and it is why heavy debit volume is the clearest signal to look at interchange-plus.
Flat does not mean uniform
Two things still move your real cost.
- Transaction size. The fixed fee is the same on every sale, so it dominates small ones. See the payment fee impact calculator.
- Situational surcharges. International cards, currency conversion and sometimes premium cards carry extra charges on top of the headline rate at most providers.
When flat rate is the right answer
For most businesses, most of the time. It is right when your volume does not justify negotiating, when your card mix is ordinary, when you value a predictable number, or when you simply do not want reconciliation to be a job. The moment to reconsider is when volume, a debit-heavy mix, or both, make the averaging expensive.
GOOD QUESTIONS
Frequently asked
Is flat-rate pricing a rip-off?+
No, though it is more expensive on average than interchange-plus. You are paying the processor to absorb the variation between cheap and expensive cards, plus the underwriting risk of onboarding you instantly. For most businesses below significant volume, that is a fair trade.
Does flat rate mean I always pay the same?+
The same rate, not the same amount. The percentage and fixed fee are constant, but your effective rate still changes with transaction size — a 2.9% + 30¢ rate costs 5.9% on a $10 sale and 3.02% on a $250 one.
Do flat rates ever have exceptions?+
Frequently. Most flat-rate providers surcharge international cards, currency conversion and sometimes premium or corporate cards. Read the situational fee list, not just the headline rate.
Which processors use flat-rate pricing?+
Stripe, Square, PayPal, Shopify Payments, Braintree and Paydude among others. Adyen and Helcim use interchange-plus; Stax uses subscription pricing; Paddle and Lemon Squeezy are merchants of record.