BEHIND THE NUMBERS
How this calculation works
Worked example
The purchases buy 10 and 5 units. £200 divided by 15 is £13.333333 per unit. At £15, those units are worth £225, a £25 unrealised gain before selling costs.
Example result: £13.33
An average of prices gives the wrong answer
Spending equal cash amounts buys more units at a lower price. The meaningful average divides total cash cost by total units rather than averaging the purchase prices.
Keep price units consistent
A UK share quote may be in pence. Convert it to pounds before entering it alongside an investment amount in pounds. Fees are entered separately so they cannot accidentally be treated as extra units.
Assumptions and rounding
- Purchases only, with fractional units and all values in a single currency.
- Fees add to the cash cost and do not buy additional units.
Questions about this calculator
Must every purchase be the same amount?
No. Each row has its own amount and price, so unequal contributions are weighted correctly.
Can I use this cost for my tax return?
Do not treat it as a UK tax basis calculator. Disposal matching and other tax rules can produce a different allowable cost.