Gold by Carat Method: Spot Price, Fineness, Coins and Tax

Every calculator on Gold by Carat calls one engine of pure functions, fed by a parameter file of legal standards, coin weights and tax rules, and by the spot price. No amount is typed into a page. The parameter file was last checked against its sources on 7 November 2026; it is updated by hand when a law, an HMRC rate or a Royal Mint specification changes.

1. The spot price

The price of a troy ounce of gold, silver, platinum and palladium in pounds comes from gold-api.com, which publishes it for each metal directly in GBP. Its terms, read on 7 November 2026, allow commercial use, forbid several requests per second and give no guarantee of accuracy. We use it as follows:

when the site is built, one request per metal, spaced more than a second apart, is saved with its time; the text of each page and the first display of each calculator use that price, and say when it was recorded (the current file: gold 11 November 2026, 12:00 am UK time);
when you open a page, your browser asks gold-api.com for the price of each metal shown on it, one request at a time at least 1.2 seconds apart; the calculator shows the time that price carries, and the amounts in the text and tables of the page are worked out again at that same price, so a weight never shows two values;
if that request fails, the calculator keeps the build price and says so, with its date and time;
nothing refreshes by itself; the “Check for a newer price” button asks again, at most once every 15 seconds.

No input you type is sent with these requests: they are plain public requests with no parameters. We do not promise any particular freshness, because it depends on gold-api.com.

2. Metal value

Value = weight in grams × fineness ÷ 1,000 × spot price per troy ounce ÷ 31.1034768. The troy ounce is 0.0311034768 kg and the grain 1/7,000 of a pound of 0.45359237 kg, per Schedule 1 of the Weights and Measures Act 1985. The tola is taken as 180 grains (11.6638 g), a South Asian trade convention with no British legal definition, and the calculator lets you change it.

3. Gold fineness by carat

Carats are converted with the standards of Schedule 2 of the Hallmarking Act 1973 and the carat table of Schedule 1: 9ct = 375, 14ct = 585, 18ct = 750, 22ct = 916.6. 24ct is valued at 999, the higher of the two pure gold standards (990 and 999). 21ct, which is not a UK standard, is valued at 875 (21/24) as a guide. Any other carat in the converter is k/24 and is labelled as not a UK standard.

4. Coins

Sovereign, half, double and £5 coins: standard weight and eleven twelfths fineness from Schedule 1 of the Coinage Act 1971 (as enacted). The sovereign’s 7.98805 g at 916.66 gives 7.3223 g of fine gold, 0.2354 oz, which matches the Royal Mint’s 0.235 oz. The quarter sovereign, the gold Britannias (1, ½, ¼ and 1/10 oz at 999.9), the silver Britannia (1 oz at 999), the Krugerrand (1 oz at 916.7) and the Maple Leaf (1 oz at 999) use the fine content in the Royal Mint’s product specifications. Older coins of other specifications are not covered; we found no official source for the silver content of older British silver coins and do not show it.

5. Offers and premiums

Share of metal = offer ÷ metal value. Premium = price ÷ metal value − 1. These are arithmetic only; the site shows no buyer’s or dealer’s prices and no “typical” rate. The default percentage in the scrap calculator is a starting value to change, not a market figure.

6. Capital Gains Tax (2026 to 2027)

UK legal tender coins (sovereigns, Britannias): sterling currency, not a chargeable asset (Taxation of Chargeable Gains Act 1992, section 21(1)(b): sterling is not an asset).
Jewellery, bars and foreign coins: chattels; exempt if sold for £6,000 or less, gain otherwise capped at 5/3 of the excess (Taxation of Chargeable Gains Act 1992, section 262: chattel exemption; GOV.UK: Capital Gains Tax on personal possessions). Foreign coins are chargeable (HMRC Capital Gains Manual CG78300: foreign currency is a chargeable asset).
Annual exempt amount £3,000; 18% within the unused basic rate band of £37,700, 24% above (GOV.UK: Capital Gains Tax rates from 6 April 2026).

The engine is tested against GOV.UK’s worked examples. It assumes no other gains in the year, does not apply loss relief and does not cover trusts, companies or non-residents.

7. VAT

Investment gold under HMRC VAT Notice 701/21: gold imports, exports and investment gold: bars of at least 995 thousandths; coins of at least 900 thousandths, minted after 1800, legal tender in their country, normally sold at no more than 180% of their gold value. Everything else is standard-rated at 20%. The calculator applies the 180% test to the price you type, as a guide; HMRC applies it to the coin’s normal selling price.

8. What is left out

Buyers’ and dealers’ prices; numismatic or antique value; stones and non-precious parts (you subtract them from the weight); historical prices (we have not confirmed a source we may republish); personal tax circumstances. Values are estimates of metal content, not offers or valuations.

Method last reviewed on 7 November 2026.