Why processors charge a percentage plus a flat fee
The two-part price mirrors the two-part cost. Part of what a processor pays is proportional to the money moved — interchange to the card-issuing bank is largely a percentage, and so is fraud loss. Part is fixed per authorisation: the network message, the settlement record, the risk screening and the dispute infrastructure cost about the same whether the charge is $4 or $4,000. A pure percentage would lose money on tiny charges; a pure flat fee would be absurd on large ones.
The consequence for you is that your effective rate is always above the headline percentage, and the gap depends entirely on transaction size. At the widely published US online card rate of 2.9% plus $0.30, a $10 sale costs 5.90% and a $1,000 sale costs 2.93%. Same rate card, twice the cost, and the only variable is the size of the basket. Anyone quoting "we pay 2.9%" without saying at what average order value is quoting the wrong number.
This also means average order value is a lever on your payment costs, not only on your revenue. Raising it from $40 to $60 cuts the effective rate at 2.9% + $0.30 from 3.65% to 3.40%, which is 25 basis points recovered without negotiating anything. Bundling, minimum order thresholds and subscription batching all work the same way, and the average order value calculator is where to size the effect on your own mix.
Published rates change and vary by product, region, card type and volume. Stripe, PayPal and Square each publish current US pricing on their own sites, and those pages — not this calculator's defaults — are the authority for what you will actually pay. Enter your own rate card here rather than assuming the defaults still apply.
The reverse calculation, and why the obvious version is wrong
Freelancers and invoicers usually want the other direction: what must I charge so that exactly $1,000 arrives? The intuitive move is to compute the fee on $1,000 and add it — $29.30, so charge $1,029.30. That is wrong, and it is wrong in a way that always leaves you short, because the processor charges its percentage on the larger amount you actually billed.
Work it symbolically. If G is the gross charge, the fee is G·r + f and the net is G − G·r − f. Setting that equal to your target N gives G(1 − r) = N + f, so G = (N + f) ÷ (1 − r). For $1,000 at 2.9% + $0.30 that is $1,000.30 ÷ 0.971 = $1,030.18, not $1,029.30. Check the naive version directly: at $1,029.30 the fee is $1,029.30 × 0.029 + $0.30 = $30.15, leaving $999.15. It is $0.85 short, and that shortfall is exactly 0.029 × $29.30 — the percentage rate charged on the fee you added.
The error is small on one invoice and structural across thousands. It also grows with the rate: at a 5% rate the naive gross-up on a $1,000 target is short by 5% of the added fee. The division form is not harder to compute, so there is no reason to use the approximation.
One caution before you pass fees on. Surcharging card payments is regulated, and the rules differ by jurisdiction and by card network — some places prohibit it outright, others cap it or require advance disclosure and signage, and network rules impose their own conditions. Building the fee into your headline price is a pricing decision and is generally unproblematic; adding a visible card surcharge at checkout is a compliance question you should check for your own market before implementing.
Worked example: a $100 sale and a $100 invoice
Take the published 2.9% + $0.30 online card rate, a domestic sale with no currency conversion.
- Percentage component. $100 × 2.9% = $2.90.
- Add the fixed fee. $2.90 + $0.30 = $3.20 total fee.
- Net deposit. $100.00 − $3.20 = $96.80.
- Effective rate. $3.20 ÷ $100 = 3.20%, which is 30 basis points above the headline rate.
- Now invoice for a $100 net. G = ($100 + $0.30) ÷ (1 − 0.029) = $100.30 ÷ 0.971 = $103.30.
- Check it. The fee on $103.2956 is $103.2956 × 0.029 + $0.30 = $2.9956 + $0.30 = $3.2956, and $103.2956 − $3.2956 = $100.00 exactly.
Compare steps 3 and 5. Receiving $100 requires charging $103.30, while charging $100 delivers $96.80 — the two figures differ by $6.50 on a $100 transaction even though the rate card is identical, because they are answers to different questions. Now add a 1.5% cross-border surcharge: the combined rate becomes 4.4%, the fee on $100 rises to $4.70, and the gross-up becomes $100.30 ÷ 0.956 = $104.92. The surcharge costs you $1.50 on the forward calculation and $1.62 on the reverse one, the difference being the fee charged on the extra amount billed.
What the effective rate tells you to do
Treat the effective rate as your real cost of accepting payment and compare it against your gross margin. On a product carrying a 20% margin, a 3.2% effective payment cost consumes a sixth of your gross profit, which puts it among your larger controllable expenses. On a 90%-margin digital product it is a rounding error. The same rate card demands entirely different levels of attention in the two businesses.
When the effective rate is far above the headline percentage, the fixed fee is the problem and the answer is transaction size, not rate negotiation. Consolidating four $25 charges into one $100 charge at 2.9% + $0.30 takes the total fee from $4.10 to $3.20 — a 22% reduction — because you pay the fixed fee once instead of four times. Monthly rather than weekly billing, order minimums and prepaid credit packs all exploit this.
When the effective rate is close to the headline percentage, your transactions are already large enough that the fixed fee barely matters, and the only remaining lever is the percentage itself. That is a volume negotiation, and interchange-plus pricing — where you pay the network's interchange plus a disclosed processor margin — usually beats blended flat-rate pricing above a certain volume because it stops you cross-subsidising expensive card types with cheap ones.
Do not forget the costs this calculator excludes. Refunds typically return the percentage but not the fixed fee, so a refunded sale is not cost-neutral. Chargebacks carry a separate per-dispute fee that survives even if you win. Payouts to a foreign bank account, currency conversion on settlement and monthly platform charges are all outside the per-transaction formula. Take the full picture into your unit economics — the margin calculators in this section are where payment cost should appear as a line, not as an afterthought.
Fee, net deposit and effective rate at 2.9% + $0.30
| Transaction | Fee | Net received | Effective rate | Charge this to net the transaction amount |
|---|---|---|---|---|
| $5.00 | $0.45 | $4.55 | 8.900% | $5.46 |
| $10.00 | $0.59 | $9.41 | 5.900% | $10.61 |
| $25.00 | $1.03 | $23.97 | 4.100% | $26.06 |
| $50.00 | $1.75 | $48.25 | 3.500% | $51.80 |
| $100.00 | $3.20 | $96.80 | 3.200% | $103.30 |
| $250.00 | $7.55 | $242.45 | 3.020% | $257.78 |
| $500.00 | $14.80 | $485.20 | 2.960% | $515.24 |
| $1,000.00 | $29.30 | $970.70 | 2.930% | $1,030.18 |
| $2,500.00 | $72.80 | $2,427.20 | 2.912% | $2,574.97 |
The last column is (amount + 0.30) ÷ 0.971. Note that it is always more than amount + fee: netting $1,000 costs $30.18, while the fee on a $1,000 charge is only $29.30.
Costs and cases this formula does not cover
- Refunds. Processors commonly return the percentage but keep the fixed fee, so a sale that is refunded still costs you money. Check your provider's refund policy — the treatment varies.
- Chargebacks. A dispute carries its own fee, typically far larger than the transaction fee, and it is usually charged whether or not you win the dispute.
- Payout and conversion costs. Settling into a different currency or a foreign bank account can add a further percentage that is separate from the transaction rate.
- Platform and marketplace commissions. Selling through a marketplace layers its own commission on top of card processing; model both together rather than separately.
- Interchange-plus versus flat-rate pricing. A blended flat rate averages cheap debit and expensive rewards cards. Your true cost mix may differ substantially from the blend.
- Micropayment and in-person rate cards. Many processors price small charges and card-present transactions on entirely different schedules. Use the right rate card for the channel.
Fitting payment cost into your pricing
Payment processing belongs in cost of goods sold, alongside shipping and packaging, not in overhead. Treating it as an administrative cost hides it from every margin calculation you run and makes low-value orders look more profitable than they are. Once it sits in cost of goods, it flows automatically into your markup and margin arithmetic and into any pricing floor you set.
If you sell through marketplaces as well as your own site, model the fee stacks separately, because the shapes differ. Marketplace fees are usually a larger percentage with a smaller or absent fixed component, while direct card processing is a smaller percentage with a meaningful fixed fee — which means the marketplace can be relatively cheaper on very small orders and considerably more expensive on large ones. The Etsy and eBay fee calculators handle those stacks, and the crossover point between channels is worth computing rather than assuming.
For service businesses that invoice, build the gross-up into your rate rather than adding it as a line item. If you need $150 an hour net and take card payment at 2.9% + $0.30, a ten-hour invoice must be ($1,500 + $0.30) ÷ 0.971 = $1,545.11 to net $1,500. Quoting $150 and absorbing the fee silently gives you $145.62 an hour, which compounds into a meaningful pay cut across a year — the freelance hourly rate calculator is where that number should be set with fees already included.