This week a payments engineer posted a break-even model for bank API pricing, and the instinct is right. HM Treasury is asking whether open banking access stays free. If you build on that rail, the question is not whether banks start charging. It is whether your margin survives if they do.

So he wrote a script. A few lines, ten minutes, everyone can put their own numbers in. The post is worth reading .

The script asks one question: at what access fee does your margin hit zero?

Read it again. It cannot answer that.

const monthlyTxns = 20 _000 ; const yourFeePence = 25 ; const otherCostsPence = 6 ;

for ( const accessFeePence of [ 0 , 1 , 5 , 10 ]) { const marginPence = yourFeePence - otherCostsPence - accessFeePence ; console . log ( ` ${ accessFeePence } p: ${ marginPence } p/txn` ); }

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Margin is linear in the access fee, and the array stops at 10. With 25p in and 6p of other costs, every row is positive: 19, 18, 14, 9. There is no zero in that list.…