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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Keep the price a customer sees and the amount sent to checkout on one shared pricing source—but do not use the same rounding rule for prices and discounts. In Daniel Pertu’s account of a TypeScript package used by a Next.js marketing site and an Expo app, list prices are buffered and rounded up, while discounts use an unbuffered rate and round down. That separation aims to make displayed charges consistent without promising a larger credit than the business intends to give.
Why one shared pricing source matters
Pertu describes a zero-runtime-dependency TypeScript package at packages/pricing, imported by both a Next.js marketing site and an Expo app. His article says 16 files import it. The design puts currency conversion and formatting in one place so that separate customer-facing surfaces can draw on the same pricing logic rather than maintain separate copies.
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The package is a project-specific implementation, not an independently tested standard. Its central design distinction is that a customer charge and a customer credit are different kinds of money movement. A helper suitable for rounding a price upward can produce an inflated discount if reused unchanged.
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How the example turns a base price into a local price
Start with fixed local prices
Pertu gives Munchable Premium’s base price as £10 per month, stored internally as 1,000 pence. He says each currency has a fixed local price rather than being converted live at checkout; €12.99 is his example of a fixed euro-area price. These are settings reported in the article, not current independently verified product prices.
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Buffer and round customer prices upward
For converted list prices, the package reportedly applies a 4% buffer (multiplying by 1.04), then rounds upward to retail-style endings. For currencies displayed with decimals, the result is rounded up to the next .99 ending. For large prices in currencies displayed without decimals, Pertu describes rounding to a scaled step, with ¥2,300 and 4,500 Ft as examples.
The article presents the buffer as a project choice associated with exchange-rate and payment-conversion costs. It also reports a 2–4% Stripe conversion-fee band, which has not been independently verified here and should not be treated as a current universal fee. Pertu’s account does not provide the exchange-rate date, so the examples should not be read as live quotes.
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Why discounts use a different conversion rule
A discount is a credit to the customer, not a new list price. Pertu says the package converts discounts using the plain mid-market rate, with no 4% buffer, and rounds down. His rationale is that rounding a credit upward could promise more value than the business intends to deliver.
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For a 20-pence reward credit, his examples are £0.20 in London and €0.23 in Dublin. Applying the list-price rule to the same small credit could instead produce €0.99, substantially overstating it. The contrast is the point: the right rounding rule depends on whether the value is charged or credited.
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Keep display precision separate from processor units
A currency’s familiar display format does not necessarily map one-to-one to the unit expected by a payment processor. Pertu reports explicit handling for zero-decimal currencies and for Stripe’s special amount-unit cases, as well as a pass-through for zero so that a free price does not become a nonzero amount after rounding.
His article identifies the following Stripe zero-decimal currencies:
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It separately lists HUF, ISK, TWD, and UGX as currencies whose Stripe amounts must divide evenly by 100 even though prices are displayed without decimals. The example given is 4,500 Ft as the displayed amount and 450,000 as the Stripe unit amount. These rules are reported from Pertu’s account; check Stripe’s current documentation for the currency and amount-unit requirements before implementing them.
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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsWhat to take from the design—and what not to generalize
The reusable lesson is to centralize the source of pricing logic while keeping charge and credit policies distinct. A single package can help multiple interfaces stay aligned, but it does not make the chosen buffer, retail endings, or tax treatment universal rules. Those are product and jurisdiction decisions that need their own validation.
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Pertu says the listed prices are tax-inclusive, with VAT taken out of the displayed amount. UK VAT treatment depends on the circumstances: HMRC guidance says an unconditional discount is accounted for using the discounted amount paid, while prompt-payment and contingent discounts have separate rules; rounding treatment also differs for invoice traders and retailers. See HMRC’s VAT Notice 700 guidance mirror and check current official guidance for tax use. Do not assume this project’s tax-inclusive presentation or discount policy applies in other jurisdictions.
Source account
The implementation details and examples above are attributed to Daniel Pertu’s article, “Prices round up, discounts round down, and one package decides both”. His account is a description of one project’s design, not a general financial rule or an independently reproduced test.
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