How to compare a South African gold offer with melt value in JavaScript

Goldza Open Source — Wed, 29 Jul 2026 11:03:00 GMT

A gold offer is easier to evaluate when the calculation is visible. The useful question is not whether a quoted rand amount sounds large, but what percentage of the item's calculated metal value remains after stated deductions.

The Goldza Fair Offer Checker turns that comparison into a small, dependency-free JavaScript calculation. The complete implementation is available in the MIT-licensed source repository.

This is a metal-only comparison. It is not an assay, jewellery valuation, buyer ranking, transaction-safety check, or financial recommendation.

The calculation

The input values are:

the live or reference price of pure gold per gram in rand;
the total item weight;
an optional estimate for stones and other non-gold weight;
the item's karat or hallmark;
the buyer's gross offer; and
any stated fees or deductions.

The calculation is deliberately explicit:

gold-bearing weight = total weight - estimated non-gold weight
fine gold grams = gold-bearing weight × karat purity
melt value = fine gold grams × pure gold price per gram
net offer = gross offer - stated fees
payout percentage = net offer ÷ melt value × 100

The project uses these purities:

Karat	Hallmark	Purity
9ct	375	37.5%
14ct	585	58.5%
18ct	750	75.0%
22ct	916	91.6667%
24ct	999	99.9%

Use the calculation engine

The versioned module can be imported directly from the public repository through jsDelivr:

import {
  calculateOffer,
  formatZAR,
} from 'https://cdn.jsdelivr.net/gh/G-O-L-D-123/goldza-fair-offer-checker@v0.2.0/src/calculate-offer.js';

const result = calculateOffer({
  pureGramZAR: 2200,
  weightGrams: 10,
  nonGoldWeightGrams: 0,
  karat: 9,
  grossOfferZAR: 6500,
  feesZAR: 0,
});

console.log(formatZAR(result.meltValueZAR));
console.log(result.payoutPercentage);

A host should replace the example price with a timestamped source and label any fallback accurately. The function returns the intermediate values as well as the final payout percentage, which makes it easier to test and explain the result.

Embed the web component

The same calculation is packaged as a standards-based custom element:

The component reads a public, timestamped price document when available and uses the labelled fallback only if that request fails. It supports common South African karats, optional non-gold weight, stated fees, shareable input links, JSON exports, and print-friendly reports.

Privacy by default

Weight and offer values stay in the browser. The project has no account requirement, analytics, cookies, server-side form, lead collection, or buyer ranking. A share link includes entered values only after the user chooses to copy it.

The output still depends on the supplied weight, non-gold estimate, karat, offer, and price. Stones, collectability, workmanship, taxes, unstated deductions, and buyer trust remain outside the model.

Try it or inspect it

A transparent formula cannot remove uncertainty from a physical item, but it can make the buyer's percentage clear before a decision is made.