Compute sales tax both ways
Add a tax rate to a pre-tax price or extract the pre-tax amount from a tax-included total. Runs entirely in your browser.
How to compute sales tax
Two modes: add a tax rate on top of a pre-tax price, or work backward from a total to extract the pre-tax amount.
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Choose direction
Add tax to a pre-tax price, or reverse extract pre-tax from a total.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
modeinpututf-8client-sidevalidatedmode · textadd · set+ tax
loaded · parsedclient-side - 02
Enter price
Type the pre-tax price or the tax-included total.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
priceoptionslivememoisedtogglesprice · memoised100 · live100.00
options set · memoisedlive - 03
Set rate
Type your local sales tax / VAT / GST percentage.
Randomness — where used — comes from
crypto.getRandomValues, neverMath.random. Heavy work sits inuseMemo.ratecomputeinstantlocaldeterministicrate · instant8.25% · computed8.25 %
computed · instantinstant - 04
Read total
Pre-tax, tax amount, and total update live with the exact formula.
Copy writes through
navigator.clipboardand downloads use aBlob— zero network traffic. Same input plus same options always yield the same bytes.copydownloadzero-networkreproducibleok · copiedready · copied108.25
shipped · ready to shipsuccess
Pro tips for everyday utilities
Reach for crypto.getRandomValues
Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.
Mock data with seeds
Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.
Reference cards beat memory
Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.
Browser APIs vary
Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.
Persist in the right place
localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.
When to use
Receipts, invoices, e-commerce checks, expense reports.
Receipt verification
Confirm the tax line on a paper or PDF receipt. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.
CSPRNG-backedInvoice prep
Compute totals before billing a client. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.
reproducibleCart estimates
Estimate checkout totals before ordering. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.
snappyVAT extraction
Pull pre-VAT amounts from gross totals for accounting. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.
feature-detectedExpense reports
Split receipts into base and tax columns. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.
deterministicInternational orders
Apply foreign GST/VAT to cross-border purchases. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.
production-readyFrequently asked questions
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