Buy Now Pay Later True Cost Calculator

What this calculator returns

The Pay-in-X BNPL model splits a purchase into a small number of equal installments at a headline rate of zero percent. The figure shown to the buyer at checkout is the sticker price divided by the number of installments. This calculator returns the actual amount paid once two costs that the headline figure hides are accounted for: any markup the merchant has built into the sticker price to cover the platform fee, and any late fees triggered by missed installments. It also annualises the cost premium against the pay-period to show the effective rate the buyer is paying — useful for comparing Pay-in-X against other short-term credit products.

How the merchant markup enters the calculation

BNPL platforms charge the merchant a percentage of each transaction, typically several percent — higher than standard card-network fees. Some merchants absorb the cost; others pass part of it through into the sticker price. The markup input lets the user model whatever pass-through assumption applies to the specific purchase. When the input is left at zero, the calculator treats the sticker as fully reflecting the merchant's underlying price; when set to a non-zero value, that share of the sticker is treated as the platform fee being paid back through the price.

How late fees enter the calculation

Most Pay-in-X plans charge a flat fee for each missed or late installment. The calculator multiplies the per-miss fee by the number of missed payments and adds the result to the total. The default of one missed payment reflects a moderate-risk scenario; setting it to zero models the case where every installment is paid on time. Stacking multiple plans, auto-debit failures, and notification gaps are common causes of misses in practice.

How the effective annual rate is derived

The cost premium — markup plus late fees — is divided by the sticker price to give a percentage cost of the purchase. That percentage is then annualised by dividing by the pay-period in years (pay-period weeks divided by 52). For a six-week pay-period, this produces an annualised figure roughly nine times the percentage cost of the transaction itself. A low-looking flat percentage on a six-week credit can translate into a high annualised rate once the brevity of the credit period is accounted for.

Why annualised matters here

The Pay-in-X disclosure typically shows zero percent APR because there is no interest charge on the credit. That is technically correct, but it understates the real cost when the headline price already includes a markup or when missed-payment fees apply. The annualised effective rate makes the BNPL cost comparable to a credit card APR, a personal loan APR, or a short-term lender APR — which all measure cost on a per-year basis. The comparison only becomes meaningful once the BNPL figure is on the same time-axis.

Where the simulation simplifies

The calculator covers Pay-in-X (short-term, zero-percent on time) plans only. Extended-term BNPL plans that charge interest on the principal — sometimes offered by the same providers for purchases above a certain threshold — require standard amortisation math instead, available in the loan and credit-card calculators in this section. Credit-score effects, collection costs after default, and overdraft fees from failed auto-debits are also outside the scope. The result should be read as the direct purchase cost under steady conditions, not a forecast of any specific account's behaviour.

Where to look next

The credit card payoff calculator runs the comparable math for revolving card debt. The loan interest cost calculator handles fixed-term installment loans. Comparing the BNPL effective annual rate against the APR on either of those two products is the most direct way to see whether the Pay-in-X offer is cheaper or more expensive than the alternative.