Buy Now Pay Later True Cost Calculator

What this calculator returns

The Pay-in-X model splits a purchase into a few equal installments at a headline rate of zero percent. What the buyer sees at checkout is the sticker price divided by the number of installments, and nothing else. This calculator returns what the purchase actually costs once two things the headline figure leaves out are counted: any markup the merchant built into the sticker to cover the platform fee, and any late fees from missed installments.

It also annualises that cost premium against the length of the pay-period, which puts the figure on the same time-axis as a credit card or loan rate. On the default scenario, a 200 purchase over four installments and six weeks with a 3% embedded markup costs 200 in cash terms, but the 6 of embedded markup works out to 3.09% of the underlying cash price and 26.80% once annualised.

How the merchant markup enters the calculation

Platforms charge the merchant a share of each transaction, and that share sits well above what card networks cost the same merchant. In the European Economic Area, interchange on consumer card payments is capped at 0.2% for debit and 0.3% for credit; published BNPL merchant pricing generally runs several times higher. Some merchants absorb the difference and some fold part of it into the sticker price.

The markup input covers whatever pass-through assumption fits the purchase. Left at zero, the calculator treats the sticker as the merchant’s underlying price and reports no premium at all. Set to 3% on a 200 purchase it treats 6 of the sticker as the platform fee coming back through the price, leaving an underlying cash price of 194. At 6% the markup doubles to 12, the cash price falls to 188, and the annualised figure rises from 26.80% to 55.32%.

How late fees enter the calculation

Most Pay-in-X plans charge a flat fee for each installment that is missed or late. The calculator multiplies that fee by the number of missed payments and adds the result to the total. The default assumes every installment is paid on time, so the total equals the sticker and the premium is the markup alone.

Raising the missed-payment count is where the number moves. On the default scenario, one missed payment at a fee of 8 takes the total from 200 to 208 and the annualised figure from 26.80% to 62.54%; two missed payments take it to 216 and 98.28%. Stacked plans, failed auto-debits and notification gaps are the usual reasons a payment slips. The calculator rejects a missed count above the number of installments, since there is nothing left to miss.

How the annualised rate is derived

The cost premium, meaning the embedded markup plus any late fees, is divided by the underlying cash price to give the premium as a percentage of what the item would have cost outright. That percentage is then scaled to a year by dividing by the pay-period expressed in years, which is the pay-period weeks over 52.

For a six-week period the scaling factor is 52 divided by 6, or about 8.7. A 3.09% premium therefore reads as 26.80% annualised. Stretch the same purchase over twelve weeks and the factor halves, taking the annualised figure to 13.40% while the cash cost stays identical at 6. Nothing about the purchase changed; only the length of time the credit was outstanding.

One simplification matters when reading the number. The scaling treats the whole cash price as outstanding for the whole pay-period, but installments reduce the balance as they are paid. On the common structure where the first installment is taken at checkout and the rest fall at even intervals, the amount actually outstanding averages roughly half the price across the period, so a balance-weighted rate would be around double the figure shown. The number here is a simple annualisation, and it errs low rather than high.

Why annualised matters here

Pay-in-X disclosure usually shows zero percent because there is no interest charge on the credit itself. That is accurate as far as it goes, and it says nothing about a markup already sitting in the price or a fee waiting on a missed payment. Annualising the premium is what makes those costs comparable to a card rate, a personal loan rate, or a short-term lender rate, all of which are quoted per year.

The comparison is directional rather than exact, for the reason above: this is a simple annualisation on the full price, while a quoted APR is calculated on the balance actually outstanding. Read the figure as a floor on the cost rather than a like-for-like rate. Regulators have been closing the gap from the other direction: the EU consumer credit rules that took effect for these products bring buy-now-pay-later schemes into the same disclosure framework as other consumer credit, including a standardised annual percentage rate.

Where the simulation simplifies

The calculator covers Pay-in-X plans only, meaning short-term arrangements that carry no interest when paid on time. Extended-term BNPL that charges interest on the principal, which the same providers often offer above a certain purchase size, needs ordinary amortisation math instead.

Payment timing is not modelled, so the calculator does not know whether the first installment falls at checkout or a fortnight later. Credit-file effects, collection costs after a default, and overdraft charges triggered by a failed auto-debit are all outside it too. What comes back is the direct cost of the purchase under the entered assumptions, not a projection of how a particular account behaves.

Where to look next

The Credit Card Payoff Calculator runs the comparable math for revolving card debt, and the Amortisation Schedule Calculator handles fixed-term installment loans. The Annual Cost of Credit Calculator puts several balances at different rates on a single annual footing. Setting the BNPL annualised figure against the rate on any of those shows where the Pay-in-X offer actually sits.