1. Simple processing fee formula
The simplest payment-fee estimate is percentage fee plus fixed order fee. In spreadsheet terms, use:
Total processing fee = revenue x percentage rate + orders x fixed fee
This works for a quick domestic-card estimate. For example, a SaaS with $10,000 in monthly revenue and 200 orders can compare a 2.9% + $0.30 model against a higher percentage merchant-of-record model. The fixed part matters because 200 small orders create more per-order cost than 20 larger invoices.
2. Blended international-card formula
If customers are global, use a blended rate instead of assuming every card is domestic:
Blended rate = domestic rate + international card share x international uplift
A product with 40% international cards and a 1% international uplift has a blended rate that is 0.4 percentage points higher than the domestic headline rate. That may be enough to change the result when comparing direct processing with merchant-of-record pricing.
3. Refund and chargeback adjustment
Refunds and chargebacks should not be ignored if the product has trials, upgrades, downloads, account sharing, or buyer confusion. A simple planning version is:
Risk adjustment = revenue x refund rate + orders x chargeback rate x chargeback fee
This does not replace a full fraud model. It simply keeps the comparison from assuming perfect customers. If disputes are common, the operational workflow can matter as much as the numeric fee.
4. Merchant-of-record comparison formula
A merchant-of-record provider usually bundles payment processing with tax handling, receipts, some buyer support, and compliance operations. A useful comparison is:
MoR premium = MoR fee estimate - direct processor fee estimate
If the premium is small, a merchant of record may be attractive because it reduces seller-side work. If the premium is large, direct processing may still win, but only if the team can handle tax, invoices, disputes, and reporting without creating hidden labor costs.
How to use the formulas
Start with current revenue and order count. Then create two future scenarios: one with higher revenue but similar average order value, and one where pricing changes from monthly to annual billing. A provider that only wins in one scenario may not be robust enough for a long-term checkout decision.
Use official provider pages for the rates. This site keeps a separate pricing-source checklist because provider fees can vary by country, product, plan, payment method, and negotiated agreement.
When formulas are not enough
Formulas are strongest when comparing visible fee lines. They are weaker when the real decision is operational. Tax registrations, invoice support, chargeback workflows, fraud review, customer receipts, and accounting exports can all change the practical winner.
If the numerical difference is small, treat the formula as a signal to inspect operations more carefully instead of treating the cheapest visible fee as the automatic winner.