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· N Khanna

3 fields decide what you pay to take a card

Mastercard publishes 2 rates for the same small business card, 0.75 of a point apart. Which one you get is decided by whether your checkout sent a sales tax amount, an invoice number and a customer reference. On an illustrative distributor putting $2,310,000 a year on business cards, that is $17,325.

A loose pencil sketch of a clipboard standing on a plain wooden desk. Its face is a grid of paper pockets, the top row holding filled slips and every pocket below it empty. Two unused paper tags hang on a hook beside it, and a thin stream of coins falls off the desk past an open green cash box instead of landing in it.
The whole thing up frontMastercard's published U.S. rate table carries 2 different rows for the same small business credit card. Data Rate I is 2.65% plus 10 cents. Data Rate II is 1.90% plus 10 cents. The only thing separating them is whether your payment software sent 3 extra fields along with the authorization. On an illustrative distributor putting $2,310,000 a year through business cards, 0.75 of a point is $17,325 a year. Your gateway will not warn you which row you are on. By its own documentation, it does not check.

When I ask to see a merchant statement, what I get handed is the first page.

The first page is a summary. Total volume, total fees, and 1 blended rate that reads like a fact of nature. Around 2.9 percent, and what were you going to do about it.

The pages behind it are where that rate comes from. They break your card volume out by interchange program, 1 row per program, with a rate against each.

That list is not a fact of nature. It is a scorecard for your own software.

The same card, 2 rates

Mastercard publishes its U.S. interchange rates as a public document. The current edition is the 2026 to 2027 U.S. Region Interchange Programs and Rates, effective April 17, 2026.

Open it to the small business credit table and read down the Business Core column.

  • Standard: 2.95% + $0.10
  • Data Rate I: 2.65% + $0.10
  • Data Rate II: 1.90% + $0.10

Same card. Same customer. Same purchase.

3 published Mastercard rates for the same small business card A bar chart of 3 rates from Mastercard's published US small business credit table, Business Core column. Standard is 2.95 percent, Data Rate I is 2.65 percent, and Data Rate II is 1.90 percent. The gap between Data Rate I and Data Rate II is 0.75 of a percentage point and is marked as the finding. Every row carries the same 10 cents per transaction, so it cancels out of the comparison. Business Core, small business credit Every row also carries 10 cents a transaction, so it cancels Standard Data Rate I Data Rate II 2.95% 2.65% 1.90% 0.75 of a point

The 3 fields

Mastercard’s own gateway documentation sets out what separates the rows. A card transaction can go out at 1 of 3 levels of detail.

Level 1 is what every checkout already sends. Date, card number, total order amount.

Level 2 is Level 1 plus what the documentation calls enhanced transaction data: customer reference number, invoice number, and sales tax amount.

Level 3 is Level 2 plus line item details.

The documentation is direct about why anybody would bother. If you accept business, corporate or purchase cards, providing Level 2 or 3 data on your transaction can qualify the transaction for better interchange rates.

Read that against the table again. 3 fields, and 0.75 of a point.

You already have all 3. The sales tax amount is on the invoice. The invoice number is the invoice number. The customer reference is the PO your customer gave you, and your salesperson typed it into the order 2 weeks ago.

They are in your system. They are just not in the message.

Which fields go out with the authorization, and which rate row that allows A left to right flow. An order in your system passes to an authorization message that carries only the 3 Level 1 fields, date, card number and order total, while the 3 Level 2 fields, sales tax amount, invoice number and customer reference, are left empty. Because those 3 are missing, the only rate row the issuer can apply is Data Rate I at 2.65 percent, and Data Rate II at 1.90 percent is out of reach. Your order has all 6 What goes over the wire date card number order total sales tax amount invoice number customer reference Rates in reach 2.65% 1.90% Data Rate I Data Rate II

The arithmetic

Take an illustrative 40-person wholesale distributor. Not a client, a model.

It takes $4,200,000 a year on cards. Its customers are other businesses, so 55% of that arrives on business cards. Call it $2,310,000.

Every one of those settles at Data Rate I, because the checkout sends 3 fields and stops.

2.65 minus 1.90 is 0.75.

0.75% of $2,310,000 is $17,325 a year.

The 10 cents a transaction is identical on both rows, so it drops out entirely. The whole difference is the percentage, and the percentage is decided by 3 fields.

$17,325 a year, for data that is already typed, already stored, and already correct.

Why it stays this way

Nobody in this chain is doing anything wrong.

Your processor is not hiding it. Mastercard’s gateway documentation states it directly: your payment service provider does not validate that the data provided on the transaction is sufficient to qualify for specific interchange rates. Nothing rejects your transaction. Nothing warns you. It goes through, it gets approved, and it settles at the higher row.

Your software vendor is not hiding it either. In Mastercard’s gateway the Level 2 and 3 fields only exist from API version 42 onwards. An integration written before that literally cannot send them, and integrations are written once and then left alone for 9 years.

And your bookkeeper cannot see it, because by the time a card fee reaches the books it is 1 number.

So the fee sits in a place where the only person who could notice it is somebody who reads the interchange breakout against the API version of a checkout, and that is not anybody’s job.

Monday

Most of this is 10 minutes.

  • Ask your processor for the interchange breakout for the last 3 months, the program-level detail rather than the summary page. They have it, they will send it, and it costs nothing.
  • Add up the volume on rows whose name contains Data Rate I, or Standard, or anything the statement calls commercial. That is your exposed number.
  • Ask whoever runs your checkout 1 question. Do we pass Level 2 data. Most of the time the honest answer is nobody has ever asked.
  • Send 1 test order through with the tax amount, invoice number and customer reference populated, and read the next statement to see which row it came back on.

That last step costs you 1 order and it settles the whole question. You do not have to trust the table or trust me. Put 1 transaction through and read which row it comes back on.

I have used Mastercard’s numbers throughout because that is the document I read and it is public. Your own statement is the authority on which programs your volume actually sits in, and it may not be the ones I have quoted.

What this is really about

A card fee looks like a price somebody quoted you. It is an output, and the input is a message your software assembles every time somebody pays you.

That is the same reason freight bills get overpaid and the same reason an order gets typed 3 times. The money is not going anywhere dramatic. It is going where a field was left empty.

So go pull the breakout. It is 1 email and it is a number you are already paying.

And if you would rather we went through it with you, the audit is 3 weeks and $2,500, and if we cannot identify $7,500 a year you do not pay. My co-founder and I take 3 a month, which is a real limit and also the reason I would rather you sent the email first.

We run this as a fixed-fee audit. $2,500, and if we find less than $7,500 a year we refund it.

See whether it fits your company