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

Liana John — Tue, 10 Nov 2026 10:43:54 +0000

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.

DEV Community: Liana John

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