What "0% interest" really costs the merchant
A 0% installment promotion is attractive to customers, but the cost doesn't disappear — it shifts to the merchant. Card networks and buy-now-pay-later providers charge a fee proportional to the installment term, and in a "0% interest" promo, the merchant has agreed to pay that fee instead of the customer. The problem is that many small businesses run these promotions without factoring this cost into their margin calculations, and end up selling at an actual loss.
This calculator computes the real cost based on your product price, installment term, the processor's fee rate, and the share of that fee the merchant covers. For example, offering a $1,000 product on a 12-month 0% plan with an 8% annualized fee rate and a 100% merchant cost share results in a real cost of about $80 — 8% of the price. If that amount isn't deducted from margin ahead of time, actual profit after the promotion can come in well below expectations.
When using a 0% installment promo as a marketing tool, it's important to bake this cost into your pricing strategy or sales targets in advance. Because fee rates tend to rise with longer installment terms, it's worth calculating and comparing the real cost of a 6-month plan versus a 12-month plan before deciding which one is worth it relative to the sales lift it drives.
Frequently Asked Questions
The installment fee that the customer doesn't pay gets billed to the merchant by the card network or financing provider instead. "Zero interest" is zero only from the customer's side — the cost still comes out of the merchant's margin.
Check the fee schedule provided by your card processor or buy-now-pay-later provider in your merchant agreement — fee rates typically rise as the installment term gets longer.
Yes. Some promotions split the fee between the processor and the merchant at a set ratio, so check your contract terms for the exact share before entering it to get an accurate real cost.