Choosing between flat rate and interchange++ pricing is one of the highest-leverage decisions WooCommerce merchants make. Get it right and you can reduce processing costs by 20–40%. Get it wrong and you’ll overpay for years without realizing it. This guide gives you a direct comparison and a framework for deciding which model fits your store.
ConvesioPay uses interchange++ pricing, all fees itemized, processor markup fixed and transparent. As a certified Adyen partner, we pass interchange and scheme fees through at actual cost. Get a cost estimate for your store →
1. How Each Model Works
Flat Rate
A flat-rate processor charges a single blended percentage for all transactions, regardless of card type, card brand, or whether a customer pays with a debit card or a premium business rewards card.
Example: 2.9% + $0.30 per transaction, regardless of what card is used.
What’s happening inside that 2.9%:
- Interchange (paid to the cardholder’s bank) — varies from ~0.05% to 3.25%
- Scheme/assessment fees (paid to Visa/Mastercard) — ~0.13–0.15%
- Processor margin — whatever’s left
The processor profits when actual interchange is low (debit, non-rewards cards) and earns a thinner margin when interchange is high (premium rewards, business cards). Over a diverse card mix, they design the blended rate to be consistently profitable.
Interchange++ (Interchange-Plus)
Interchange++ passes through the actual interchange and scheme fees at cost, then adds a fixed processor markup on top.
Example: Interchange + scheme fees + 0.25% + $0.10 per transaction.
Each component is visible on your statement. You pay what interchange actually costs for each card type, not a blended average. The processor earns only their fixed markup — nothing more.
2. Side-by-Side Comparison
| Flat Rate | Interchange++ | |
|---|---|---|
| Fee structure | Single blended % | Actual interchange + scheme fees + fixed markup |
| Predictability | High — same rate every transaction | Varies by card type, predictable markup |
| Transparency | Low — margin hidden in blended rate | High — all components visible |
| Cost at low volume | Reasonable — simplicity worth the premium | Comparable, sometimes slightly higher |
| Cost at high volume | Often significantly more expensive | Lower — especially with diverse card mix |
| Comparison shopping | Difficult — can’t compare components | Easy — compare markup directly |
| Best for | New stores, very low volume (<$5K/month) | Growing stores processing $10K+/month |
3. The Cost Difference in Practice
The gap between flat rate and interchange++ depends on your card mix. Let’s model a WooCommerce store processing $30,000/month with a typical US consumer card mix:
| Scenario | Flat rate (2.9% + $0.30) | Interchange++ (actual + 0.25% + $0.10) |
|---|---|---|
| $30,000/month, 200 transactions | ~$930/month | ~$785–$810/month |
| Annual cost | ~$11,160 | ~$9,420–$9,720 |
| Annual savings | — | ~$1,440–$1,740 |
ConvesioPay Q1 2026 data shows merchants switching from blended/flat-rate pricing to interchange++ save an average of 0.38% of processing volume. The savings increase as volume grows and as a larger share of transactions come from lower-interchange card types (debit, non-rewards).
4. When Flat Rate Makes Sense
Flat rate isn’t always the wrong answer. It’s appropriate when:
- Volume is very low — below $5,000/month, the savings from interchange++ are often less than $20/month; the predictability of flat rate may be worth it
- You’re just starting out — flat rate processors (Stripe, Square, PayPal) are instant to set up with no underwriting; interchange++ providers sometimes require a brief onboarding review
- Transaction sizes are very small — the per-transaction fee structure of interchange++ can be less favorable for very high-frequency, low-value transactions
- Your card mix skews heavily toward premium rewards/business cards — the flat rate spread narrows with high-interchange cards, reducing the relative advantage of interchange++
5. When Interchange++ Makes Sense
Interchange++ is usually the right choice when:
- You process $10,000+/month — the savings become meaningful at this threshold
- You have a diverse or debit-heavy card mix — you’re paying 2.9% on cards that actually cost 1.2–1.8% in interchange
- You want cost transparency — you can verify every fee and audit your processor’s charges
- You’re scaling — the gap between flat rate and interchange++ widens as volume grows
- You want to compare processors fairly — markup is directly comparable; blended rates are not
6. The Third Option: Tiered Pricing
Some processors use tiered pricing, where transactions are classified as “qualified,” “mid-qualified,” or “non-qualified” based on criteria the processor controls. Avoid this model:
- Qualification criteria are set by the processor, not disclosed to merchants
- Premium cards often “downgrade” to non-qualified tiers with significantly higher rates
- You have no way to predict or audit your costs
- Total cost is typically higher than both flat rate and interchange++ at any meaningful volume
If a processor quotes tiered pricing, treat it as a red flag and ask for interchange++ pricing instead.
7. How to Make the Switch
Moving from flat rate to interchange++ doesn’t require rebuilding your checkout. ConvesioPay’s WooCommerce plugin installs in minutes and replaces your existing payment gateway, the switch happens at the processor level, not the checkout level.
To evaluate whether the switch makes sense for your store:
- Find your current processing volume (from your last statement)
- Find your current effective rate: total fees ÷ total volume × 100
- Compare against the interchange++ rate for your volume tier
- Calculate annual savings
For more detail on fee components, see Credit Card Processing Fees Explained. For a full breakdown of interchange++ pricing, see Interchange++ Pricing: Why Transparent Processing Saves You Money.
See what you’d pay with interchange++ pricing. Share your current volume and card mix and we’ll run a comparison. Talk to our team →