A payment processor authorizes, captures, and settles card and ACH transactions on behalf of a merchant.
A payment gateway is the software layer that connects a merchant’s checkout — whether on a website, in an app, on a phone, or in person — to the processor and the card networks.
Modern full-stack processors like Stripe, Square, and PayPal combine the processor and the gateway into one service; older configurations like Authorize.Net plus a legacy merchant-account processor (First Data, TSYS, Worldpay) separate the two.
Run a quick stress-test: when you set up Stripe on a WooCommerce store, you are configuring both the payment gateway (the WooCommerce Stripe Payment Gateway plugin on your server) and the processor (Stripe’s merchant account, bank account registration, and underlying card-network connection) at the same time.
When you set up Authorize.Net with a legacy merchant account, you are configuring the gateway (Authorize.Net) and the processor (the merchant account provider) separately, and the gateway forwards transaction requests to the merchant account for authorization.
A payment gateway is the bridge between your checkout and the processor; the processor is the bridge between your gateway and the card networks. Full-stack processors like Stripe, Square, and PayPal collapse both into one service. Legacy configurations like Authorize.Net plus a merchant-account provider separate them.
Key facts: A payment gateway reads card details (or tokenized card reference) from your checkout and forwards the authorization request to the payment processor.
The processor routes to the card network (Visa, Mastercard, Amex, Discover), which forwards to the issuing bank for approval or decline.
The processor captures and settles the net funds to your merchant bank account.
Modern full-stack providers (Stripe, Square, PayPal, Braintree, Adyen) handle both functions in one stack.
Legacy setups (Authorize.Net + Worldpay/First Data merchant account) split them.
Most small businesses today use a full-stack provider and never need to distinguish the two layers.
For 95% of small businesses taking card payments, the distinction between gateway and processor is invisible: Stripe, Square, or PayPal handles both. The distinction matters for ecommerce stores on legacy platforms (Shopify, WooCommerce, Magento) integrated with a separate gateway provider (Authorize.Net, NMI) plus a merchant-account processor (First Data, Worldpay, TSYS).
The three layers of a card transaction
Every card transaction flows through three layers. Understanding each layer clarifies when the gateway/processor distinction matters.
Layer 1: merchant’s checkout. Where the customer enters card details. WooCommerce checkout page, Shopify checkout page, Square POS reader, Stripe Checkout form, PayPal Commerce button. This is where the data is captured and encrypted.
Layer 2: gateway. Software that encrypts card details, formats the transaction request, and forwards to the processor. Examples: Stripe’s hosted form, Square’s POS software, Authorize.Net’s API, NMI’s gateway. The gateway does not move money; it routes and formats requests.
Layer 3: processor + card networks + issuing bank. The processor (Stripe, Adyen, a legacy merchant account provider) holds the merchant account.
The processor routes the request to the card network (Visa, Mastercard), which forwards to the issuing bank (the customer’s bank) for authorization.
The processor captures the funds, holds them in the merchant account, and settles to the merchant’s bank account on the payout schedule.
The distinction between gateway and processor matters most when one is bundled into the other (full-stack) or when they are separate (legacy setups).
Full-stack processors: when gateway and processor are the same
Modern processors (Stripe, Square, PayPal via Braintree, Adyen, Checkout.com, Mollie) bundle the gateway into their product. You set up a Stripe account, install the Stripe plugin or SDK on your store, and Stripe does the rest. The processor handles both your checkout integration (gateway layer) and your merchant-account settlement (processor layer).
| Full-stack provider | Gateway role | Processor role | Best for |
|---|---|---|---|
| Stripe | Stripe Checkout, Stripe Elements | Stripe-managed merchant account under own bank partner | SMBs, SaaS, marketplaces, ecommerce |
| Square | Square Checkout, Square Online, Square POS | Square-managed merchant account under Wells Fargo banking partnership | Retail, food service, professional services |
| PayPal Commerce / Braintree | PayPal Commerce button, Braintree Drop-in UI | PayPal-managed merchant account | Ecommerce with PayPal-first buyer persona |
| Adyen | Adyen Drop-in / Components | Adyen-managed; bank partner varies by country | Enterprise; not SMB-typical |
The full-stack approach simplifies operations (one vendor, one contract, one reconciliation, one support path) at the cost of less pricing flexibility and less provider portability.
Separated gateway + merchant account: the legacy pattern
Pre-Stripe (and pre-Square), the standard payment stack was a separated gateway plus merchant account. The gateway (Authorize.Net, NMI, USAePay) provided the software to capture and forward; the merchant account (First Data, TSYS, Worldpay, Global Payments) provided the bank-side funds holding and settlement.
This pattern persists for two reasons. First, businesses with high-volume interchange rates can negotiate with the merchant account provider, with the gateway as a pass-through. Second, businesses already on legacy infrastructure (e.g., a Magento 1 store integrated with Authorize.Net since 2014) don’t migrate to a full-stack provider easily.
The trade-off is operational complexity: two contracts, two monthly statements, two support paths, and a wire (gateways charge a separate fee to the merchant account for the connection).
Why you rarely need a separated setup
For most small businesses, a full-stack provider is the right answer. Three situations where separated setup is genuinely needed.
Very high volume with custom interchange-plus pricing. At $500k+/month, you can negotiate interchange-plus pricing directly with a merchant account provider. The savings versus Stripe (effective 2.9% + 30 cents) can be 0.4%-0.7%, which is $2k-$3.5k/month. Use an interchange-plus processor (Stax, Payment Depot) that wraps the same merchant account provider with a software UI; the merged entity model is still full-stack.
High-risk MCC that requires an explicit merchant account. Some merchant category codes (firearms, adult entertainment, nutraceuticals, debt collection) are above the underwriting threshold for Stripe, Square, and PayPal. They require a high-risk merchant account provider (Radius Bank, eMerchant, BankCard USA). The gateway (typically Authorize.Net or NMI) is configurable to that merchant account.
Multi-acquirer routing for redundancy. Some platforms (large SaaS) route transactions across multiple acquirers (Stripe plus Adyen) for redundancy against a single-acquirer outage. This is enterprise; SMB need not consider.
Where the gateway role shows up in modern full-stack processors
Even with a full-stack provider, the gateway role is still inside the product; you just don’t configure it separately.
For Stripe: the gateway role lives in Stripe.js (for card tokenization without PCI scope), Stripe Elements (for hosted form fields), Stripe Checkout (for the hosted page experience), and Stripe Terminal (for in-person hardware). The Stripe plugin for WooCommerce or Shopify bundles all three plus the merchant account configuration.
For Square: the gateway role lives in Square’s Web Payments SDK (online), Square POS Software (in-person), and Square Reader hardware. A single Square account configures all four.
For PayPal Commerce: the gateway role lives in PayPal’s Smart Buttons or Braintree Drop-in. PayPal’s hosted payment experience is similar to Stripe Checkout, with the additional PayPal wallet recognition at checkout.
What changes in the decision when you have a non-US business
The gateway/processor distinction matters differently outside the US. Outside the US, full-stack processors are often the only option for small businesses; legacy merchant-account setups vary by country. Stripe and Square are full-stack globally; Adyen is the dominant acquirer for enterprise; Worldpay operates in the UK and EU. For a non-US founder selling to US customers, Stripe (which holds US banking partners) is the canonical answer.
For a US LLC owned by a non-resident, Stripe Atlas includes a Delaware LLC formation + EIN + US bank account + Stripe merchant account all wired up; this is the canonical pattern for foreign founders. Square and PayPal each support foreign-owned US LLCs but require more document upload.
What to ask your provider
For a small business evaluating a payment processor, three questions are worth asking in writing before signing.
“Is this provider full-stack or am I connecting a separate gateway?” Confirms whether you need to configure and pay for an Authorize.Net (or equivalent) on top.
“What interchange category are my expected transactions in, and what’s the published rate per category?” Forces the provider to commit to specific card-type pricing instead of generic “starting at” language.
“Are there any reserve holdback or rolling reserve requirements at my volume and category?” Surfaces hidden capital exposure for high-risk or new-business merchants.
Pick the structure that fits your scale
The decision follows three rules of thumb.
Use a full-stack processor (Stripe, Square, PayPal) for any small business with under $50k/month in volume. The operational simplicity is worth more than the negotiated interchange savings you’d get at scale.
Move to an interchange-plus processor (Stax, Payment Depot, Helcim) when volume exceeds $50k/month and your card mix is dominated by debit and low-cost credit cards. The savings are real; the operational complexity is contained.
Move to a separated gateway + merchant account only when you have a specific reason (high-risk MCC, multi-acquirer routing, enterprise volume). The operational complexity is real.
For the cost math at each tier and the card-type-by-card-type breakdown, the payment processing fees page runs the full numbers.
For the broader provider comparison (Stripe, Square, PayPal, Stax, Helcim, plus the high-risk carve-outs), the best payment processor for small business comparison goes through each.
For the practical 3-way on Stripe vs Square vs PayPal on dimensions beyond pricing (API quality, in-person hardware, consumer trust), the stripe vs square vs paypal page covers the difference.
For the end-to-end flow of a card transaction including the authorization capture settlement payout cadence and the four non-negotiables every processor must do the how payment processors work page walks through each step.
Last updated: October 2026
