Buy Now Pay Later Calculator

This calculator handles both of the two structurally different BNPL products in one model. When you set the annual interest rate to 0% — the classic "Pay-in-4" plan used by Afterpay and Klarna's short installment option — the payment amount is simply the purchase price divided evenly across installments, and the only cost beyond the sticker price comes from late fees on any payments you expect to miss. When you enter a nonzero APR — the longer-term monthly installment plans offered by Affirm and Klarna for bigger purchases — the calculator switches to a standard loan amortization formula to compute the true payment amount and the interest embedded in it, the same way it would for an auto loan or mortgage. From the consumer's total cost (purchase price plus interest plus any late fees), the calculator backs out an effective APR: the annualized true cost of financing, useful for comparing a BNPL plan against putting the same purchase on a credit card.

This is worth watching closely, because a plan advertised as "0% interest" can still carry a real effective cost once late fees are factored in for a borrower who's likely to miss a payment or two. On the merchant side, the calculator applies a separate merchant discount rate — typically 4-8% of the purchase price — to show what the retailer actually nets after paying the BNPL provider for offering the option, which is a meaningfully higher cost than standard card processing fees (usually under 3%) in exchange for higher conversion and average order value. One assumption worth flagging: missed payments are modeled as a flat count entered by the user rather than a probability distribution, so the late-fee total is only as realistic as your own estimate of how many payments you expect to actually miss.