When 'cheapest' is just a poor structural fit
The calculator already flags the worst structural mismatches in the notes column. SumUp gets a 'strongest for in-person' note when picked for online-only businesses. Wise Business gets a 'best for invoicing' note when picked for B2C card-present.
If the cheapest row has a structural-fit note attached, treat the cost ranking as informational rather than a recommendation. The next-cheapest row without a fit warning is usually the right choice.
When migration cost eats the savings
Switching providers has a real cost — developer time to re-integrate, a few weeks of operational tail, and the risk of broken edge cases on the cutover. For a small online business that cost is typically 2,000 to 8,000 in time and disruption.
If the projected annual saving is under 5,000, the migration usually does not pay back inside 12 months. Stay where you are unless you are also switching for a non-cost reason — better dispute tools, better FX handling, an integration you actually need.
When operational cost outweighs fee savings
Some providers cost less per transaction but more in time. Slow settlement (T+5 versus T+2) ties up cash. Weak dispute tools mean more time per chargeback. Poor accounting integration means more reconciliation work.
An owner whose time is the binding constraint should weigh time cost like fee cost. Five extra hours a month at a realistic owner-rate is often worth more than 0.3 percent in fee savings.
When buyer trust drives conversion
On consumer-facing checkouts, offering PayPal as a payment option still meaningfully lifts conversion in some markets even though PayPal's fees are higher than Stripe's. The lift can be larger than the fee gap. The calculator does not see this — it compares cost on a fixed assumption that volume stays constant.
If your business is consumer-facing and international, run the calculator without PayPal and with PayPal as a secondary option, then ask whether the extra fee is plausibly offset by extra conversions.
How to use the calculator output well
Use the cost ranking to identify the two or three realistic candidates, not to pick a winner. Read the structural-fit notes and the observation list to filter out poor fits. Then weigh migration cost, operational fit, and any conversion-lift considerations on top.
The calculator gives you the financial half of the answer. The other half is judgement about your specific business — and the calculator is built to make that judgement easier rather than to replace it.