Max MorrishBack to projects

SellerShock

Two browser calculators for Amazon sellers facing the 2026 DD+7 payout delay and a fee surcharge.

Demo build, April 2026. Screens and video come from a copy with checkout turned off.

12 days from sale to cash for the example seller: 5 days to deliver plus 7 days of reserve

31 seconds in the demo build: loading a preset, raising the cash buffer, running a $24.99 product through the surcharge calculator, then switching to the thin-margin preset.
Where
Personal project
Role
Product and build
Built with
Next.js 16, React 19, TypeScript, Tailwind CSS, node:test

What I made

In spring 2026 Amazon sellers faced a DD+7 reserve, which holds payouts until seven days after delivery, and a 3.5% surcharge on FBA fulfillment fees.

I built SellerShock in April 2026: a Next.js static site with a cash-gap planner for DD+7 and a surcharge calculator. Everything runs in the browser on the seller's own numbers, with no Seller Central login.

  1. Seller's numbersrevenue, delivery lag, margins, cash buffer, or price and volume
  2. Calculator mathtwo pure functions, 22 unit tests
  3. Resultdays to cash, cash gap, monthly surcharge hit, price move
  4. Next movea written recommendation; checkout is off in this demo
From a seller's numbers to an answer. Nothing connects to Seller Central.

22unit tests passing on the calculator math

14seller inputs across the two calculators

2calculators: DD+7 cash gap and 3.5% surcharge

What came out of it

The cash gap

On the example inputs, money arrives 12 days after a sale, with $6,000 already spent on stock and ads for those sales: $1,000 more than the $5,000 cash buffer.

DD+7 cash gap planner with example inputs: $60,000 monthly revenue, $32 average order, 5-day delivery lag, 7-day reserve window and a $5,000 cash buffer. Results: 12 days to cash, $24,000 of revenue tied up, $6,000 cash exposure, a $1,000 reserve gap and a medium risk badge.
The cash gap planner on example inputs: 12 days to cash and a $1,000 gap on a $5,000 buffer.
SellerShock at 390 pixels wide on a phone: the last cash gap inputs (18% COGS, 7% ad spend, $5,000 buffer) and the first results, 12 days to cash and $24,000 of revenue tied up.
The same planner at phone width.

The demo build

Every checkout link in the demo is replaced by a disabled button.

SellerShock landing page on desktop: the headline 'See your cash gap, margin hit, and next move before policy pain turns into cash pain', an operator snapshot panel with the two policy dates, and a header button reading 'Checkout disabled in demo'.
The landing page. The header button reads 'Checkout disabled in demo'.

Where it's going

The full version is a toolkit for Amazon sellers: calculators, maintained worksheets, and an importer and scenario updater for when fee or payout rules change, all on the seller's own numbers with no Seller Central login.

  1. NowDemo buildA cash-gap planner and a surcharge calculator in the browser.
  2. Surcharge maths matchedThe surcharge calculator applies the fee the way Amazon does.
  3. Maintained worksheetsRepricing and reserve-planning worksheets and a response checklist, kept current.
  4. Importer and updaterAn importer, and a scenario updater that reruns numbers when rules change.
  5. Seller toolkitCalculators, worksheets and rule updates together, on the seller's own numbers.