[Solved] PHP: How to create a linear function, calculating a credit card fee? [closed]

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I’ve got what you want, so think in this way:

  1. you have original price
  2. you want to calculate final transferAmount

that:

transferAmount = originalPrice + fee

but fee here depends on transferAmount

fee = transferAmount * 0.029 + 2.25

now solve it:

transferAmount = originalPrice + transferAmount * 0.029 + 2.25
transferAmount*(1-0.029) = originalPrice + 2.25
transferAmount = (originalPrice + 2.25) / (1-0.029)

in php:

$price = 10;
$total = ($price + 2.25) / (1.0 - 0.029); // 12.615859938208033
$fee = $total - $price; // 2.6158599382080325

now you can verify:

12.615... * 0.029 + 2.25 = 2.615...

ie, merchant will take 2.615... as fee and result is 10

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solved PHP: How to create a linear function, calculating a credit card fee? [closed]