Interchange-plus vs flat-rate, with the break-even math
If you process more than $15,000/mo, interchange-plus almost always wins. Below that, flat-rate's simplicity is worth the markup. Here's why — and the exact numbers.
✓Editorially reviewedReviewed by Sam Patel, Merchant services editorUpdated April 1, 2026How we make moneyMethodologyAdvertiser disclosure
Quick answer
Most US small businesses hit break-even between $10k and $20k/mo in card volume. Above $20k, interchange-plus saves $200-$600/mo. Below $8k, flat-rate's simplicity is usually worth the small premium.
What each model actually charges
| Criteria | Flat-rate (Square, Stripe) | Interchange-plus (Helcim, Stax) |
|---|---|---|
| Headline rate | 2.6% + $0.10 (in-person) | Interchange + 0.30% + $0.10 |
| Effective cost on $10k/mo | ~2.7% = $270 | ~2.3% = $230 ✓ |
| Effective cost on $50k/mo | ~2.7% = $1,350 | ~2.1% = $1,050 ✓ |
| Statement complexity | One line per transaction ✓ | Three lines per transaction |
| Predictability | Identical % every month ✓ | Varies with card mix |
| Hidden markup risk | None | None (markup disclosed) |
| Setup time | Same day ✓ | 1-3 business days |
The break-even math
Flat-rate processors bundle interchange + assessments + markup into one number. Their margin is highest on debit cards (where interchange is low) and lowest on rewards cards (where interchange is high).
For a typical small business with a 70/30 credit/debit mix and $50 average ticket:
- Flat-rate: 2.6% + $0.10 = 2.80% effective at $50 ticket.
- Interchange-plus: blended interchange (~1.65%) + assessments (~0.13%) + markup (0.30% + $0.10) = 2.28% effective.
- Savings: 0.52% × monthly volume. At $20k/mo = $104/mo. At $50k/mo = $260/mo.
Most interchange-plus processors charge a $20-30/mo statement fee. So your true break-even is wherever monthly savings > monthly fees — usually around $10-15k/mo.
Which one is right for you?
Stay on flat-rate if…
- • You process under $10k/mo in cards
- • You value zero monthly fees over rate
- • You want one simple number on every statement
- • You're new and don't know your card mix yet
Switch to interchange-plus if…
- • You process over $15k/mo
- • Your average ticket is over $75
- • You're B2B (level-2/3 data savings)
- • You can stomach a 3-line statement
FAQ
For most US businesses, interchange-plus wins above $15,000/mo in card volume — sometimes as low as $8,000/mo if your average ticket is large.
See your real break-even number
Plug in your monthly volume and average ticket — we'll show you which model wins.