I built a tiny tool for the problem every BNPL app hides: the stack

Every buy-now-pay-later app answers one question well: "What do I owe you?" None of them answer the question that actually bites: "What do I owe everyone, and when?"

Run Klarna for a jacket, Afterpay for shoes and Affirm for a laptop and you have three dashboards, twelve installments and four different due-date rhythms — pay-in-4 every two weeks here, a pay-in-30 lump there, a longer financed plan underneath. Each app is individually honest. The stack is invisible anyway.

So I built BNPL Stack Untangler — a small, free web tool with one job: take the plans you already have and render them as a single picture.

What it does

• You enter each plan once: provider, item, installment amount, remaining payments, due dates.
• It shows the combined view no provider shows: total owed across all plans, what's due this week and this month, and the calendar of upcoming installments across providers.
• It flags the collision weeks — the pay cycles where several plans land together — and the plans carrying late-fee exposure if a payment slips.

Design choices worth mentioning

• No account-first wall. The point of the tool is a quick reality check; making people register before they can see their own total would defeat it.
• Provider-agnostic by design. The tool doesn't integrate with any BNPL provider's API — deliberately. The stack exists across providers, so the input has to be the user's own list, not one company's feed.
• The guides carry the detail work. The fee and plan differences live in written guides — late fees compared, Klarna vs Afterpay vs Affirm, and a holiday BNPL guide — so the tool itself can stay a single screen.

The interesting lesson from building it: the hard part wasn't the maths, it was the calendar. Stacked plans don't fail because the totals are huge — they fail in one specific week where everything lands at once. Any tool in this space that shows totals without a timeline is missing the actual failure mode.

If you juggle more than one BNPL plan, the untangler is free: https://bnplstackuntangler.com — and I'd genuinely like to hear what view of your stack would help most.