Several purchases at different prices make your real cost hard to see. Here is the right way to combine them, with a worked example and the mistake to avoid.
Short answer: add up everything you paid and divide by the total grams you own. Do not average the per-gram prices, because that treats a small purchase and a large one as equal. For three purchases totalling 91.1 g for 5,890, the average cost is about 64.65 per gram.
Average cost per gram equals total cost divided by total grams. Total cost should include the premium, shipping and fees, so it reflects what the metal really cost you. This is your cost basis spread across your weight.
Total weight is 91.1 g and total cost is 5,890, so the average is 5,890 ÷ 91.1, about 64.65 per gram. The per-gram prices were 62.7, 64.0 and 66.0, and their simple average, 64.2, understates the true figure because the dearest purchase was the largest.
Divide the spot price per troy ounce by 31.1035 to get spot per gram, using the price per gram calculator. If spot per gram is above your average, your holding shows a gain, before any selling costs.
Gold, silver and platinum each need their own average. Mixing them gives a number that means nothing.
The average cost calculator combines up to ten purchases and shows your gain or loss. BullionKeeper does the same automatically for every holding as you record it, so the average stays current without any spreadsheet work.
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