Buy Now Pay Later (BNPL) Calculator

The standard Pay-in-4 product offered by Affirm, Klarna, Afterpay, and Sezzle is 0% interest as long as every installment lands on time. There is no rate, no origination fee, and no penalty for paying early. You split the purchase into four equal payments due every two weeks, with the first taken at checkout. The catch is that the offer is conditional: miss one installment and the cost stops being zero, either through a late fee (Klarna, Afterpay, Sezzle) or a damaged credit score (all of them now report some plans to the bureaus). Longer-term BNPL is a different product entirely (see the next question).

Once you cross the 6-week Pay-in-4 line into a longer-term installment loan, BNPL becomes an interest-bearing product just like any other consumer loan. Affirm's 3, 6, and 12-month plans range from 10% to 36% APR depending on your credit profile and the merchant subsidy, with the rate shown upfront at checkout. Klarna's 'Financing' product (formerly Slice It) runs in the same 7.99% to 33.99% APR range. Apple Pay Later (now wound down) and Afterpay Plus card extensions also charge interest above the 4-installment threshold. The longer the term, the higher the rate tends to be.

Late-fee policies vary by lender. Klarna charges up to $7 per missed installment with a cap at 25% of the original order value. Afterpay caps late fees at $8 per missed payment with a hard ceiling of 25% of the order, and pauses new purchases on your account until you are current. Sezzle charges a $15 reschedule fee but waives it if you postpone via the app before the due date. Affirm is the outlier: it charges no late fees on any of its plans, but it does report late Pay-in-4 payments to Experian, which is arguably worse than a one-time fee.

Yes, increasingly. As of 2025, all three major US credit bureaus (Experian, TransUnion, and Equifax) accept BNPL data, and FICO Score 10 and VantageScore 4.0 both incorporate it. Affirm reports every Pay-in-4 plan to Experian. Klarna reports Pay-in-4 to TransUnion and longer-term financing to all three. Afterpay began reporting select Pay-in-4 plans in 2024 and reports all longer-term plans. The net effect is that a missed BNPL installment can ding your score the same way a missed credit-card payment does, while reliably paid BNPL can build thin credit files. Treat every BNPL plan as if it shows up on your credit report, because it now usually does.

A 2023 Stanford University study of retail-app data found shoppers spent 35% more per order when BNPL was available at checkout than when it was not, and the lift was largest on discretionary items like fashion and electronics. The mechanism is straightforward: splitting a $400 purchase into four payments of $100 each makes the price feel smaller, the way a $9.99 sticker feels much smaller than $10. The CFPB has documented the same pattern, including higher rates of overdrafts and parallel card debt among heavy BNPL users. Run any BNPL purchase through this calculator first. If you would not buy it in cash today, the installment plan does not make it more affordable, it just hides the cost.