Flat rate pricing is a payment processing model where merchants pay the same percentage fee on every transaction, regardless of the card type used. Square charges 2.6% + $0.10 for in-person swipes; Stripe charges 2.9% + $0.30 for online transactions. These rates don't change whether a customer uses a basic debit card or a premium travel rewards card.
The appeal of flat rate pricing is simplicity. You know exactly what you'll pay per transaction. There are no surprises from interchange categories, no qualification tiers, and no complex statements. This makes flat rate ideal for new, very small, or low-volume businesses that value predictability over optimization.
The significant downside is cost. Flat rate processors set their rates above the average interchange cost so they profit on every transaction type. When a customer pays with a basic debit card (interchange ~0.05% + $0.22), the processor captures nearly the entire flat rate as profit. Merchants pay the same rate on low-cost transactions as on high-cost ones, which means they're subsidizing the processor's margin on cheap card types.
For businesses processing over $10,000-$15,000 per month with a diverse card mix, interchange plus pricing almost always saves money. The crossover point depends on your transaction mix and average ticket size.
Major flat rate providers include Square, Stripe, PayPal, and Shopify Payments. These companies built their businesses on ease of use and are excellent for startups, but become expensive as volume grows.
Flat rate pricing is rarely the cheapest option for established businesses. A restaurant processing $60,000/month on Square (2.6%) pays $1,560 in fees. The same volume under interchange plus pricing at an effective rate of 1.9% costs $1,140 — saving $420/month or $5,040/year.
The key question: how much do you value simplicity over savings? For very small businesses, the management overhead of understanding interchange may not be worth the savings. For businesses grossing over $500,000/year, optimizing your payment processing is a meaningful financial lever.
A coffee shop processes $25,000/month. Customer mix: 40% debit cards, 60% credit cards. - Under flat rate (2.6%): $650/month - Under interchange plus (actual costs + 0.25% markup): - Debit cards: ~0.5% effective = $50 - Credit cards: ~2.0% effective = $300 - Total: $350/month - Monthly savings: $300 - Annual savings: $3,600
Flat rate pricing is excellent for businesses just starting out or processing under $5,000/month. The simplicity and no monthly fees make it accessible. As volume grows, the math favors switching to interchange plus pricing.
Square charges a premium for simplicity, instant setup, no monthly fees, and no merchant account underwriting. They profit on the difference between actual interchange costs (which average around 1.7-1.9% for credit) and their flat rate. For high-volume merchants, this premium becomes significant.
Large-volume merchants (over $250,000/year) may be able to negotiate custom rates with Square or Stripe. However, these platforms are not designed for custom interchange plus pricing, so negotiations are limited.
Consider switching when your monthly processing volume exceeds $10,000-$15,000 consistently, or when you calculate that the savings from interchange plus would exceed $200/month. A free statement analysis can tell you your exact breakeven point.
If you're currently on Square or Stripe, Liberty Bancard can show you exactly what you'd save with interchange plus pricing — before you switch. We do a free side-by-side comparison using your actual statements.
Most merchants who switch from flat rate to Liberty Bancard save between $300–$1,000+ per month depending on volume and card mix.
Continue learning: Browse all 60 payment processing terms in our Payment Processing Glossary, or upload your statement for a free analysis of your current processing costs.