Cost Basis & Share Matching Calculator

About the Cost Basis & Share Matching Calculator

When you sell shares bought at different times and prices, your tax rules decide which purchases each sale is matched with — and so the cost, the gain or loss, and what is still held. This calculator applies the rule of your country to your own trades: the UK’s share identification rules (same day, then the next 30 days, then the Section 104 pool), Canada’s adjusted cost base with the superficial-loss rule, US lot identification with wash sales, first in, first out for Germany and India, and for other markets first in, first out or the average cost of identical shares, whichever your tax rules use.

Load the trades file your broker exports (or type the trades), choose the rule, and see every sale with the purchases it was matched to, the rule that matched them, the cost, the proceeds and the gain or loss, the wash-sale or superficial-loss flags with the adjusted cost, the holding after every trade and the totals for each tax year — with a CSV for the country capital-gains calculators.

Trades in another currency are converted with the rates you give: one for each currency, or one on each trade you type. Your trades are read in your browser and never uploaded.

Common uses

• Work out the gains and losses of a year of share sales for a UK return, with the 30-day rule and the Section 104 pool applied to every sale.
• Check the adjusted cost base of shares you bought in several lots before selling part of them in Canada.
• See whether a loss you took was a wash sale because you bought the shares back within 30 days.
• Turn a broker’s trade history into one line per sale for a capital-gains calculator or an accountant.

The rules

• United Kingdom. Shares sold are matched first with shares of the same company bought on the same day, then with shares bought in the 30 days after the sale (the “bed and breakfast” rule, which does not apply to shares bought while you were not UK resident), then with the Section 104 holding — all your other shares of that company at their average cost — and finally with later purchases, earliest first (CG51555, CG51560, helpsheet HS284). All sales of one day are one disposal. When several purchases fall in the 30 days, the tool takes them in date order, earliest first.
• Canada. The adjusted cost base is the average cost of all your identical shares, worked out again at each purchase, commissions included; a sale’s gain is its proceeds minus its outlays minus the ACB of the shares sold (CRA guide T4037). A loss is superficial when you (or an affiliated person) buy identical shares in the 30 days before or after the sale and still hold them 30 days after it: the loss is denied and added to the ACB of those shares (Income Tax Act, section 54).
• United States. The shares sold are those you identify; without identification, the first ones bought. Average basis is for mutual fund shares. A loss is disallowed under the wash-sale rule when you buy substantially identical shares within 30 days before or after the sale; it is added to the basis of the shares bought, and their holding period includes that of the shares sold (Publication 550). Each lot sold counts on its own, so a lot sold at a gain keeps its gain; the replacement shares are taken in the order bought and paired with the shares sold at a loss, which are taken in the order they were bought (Treasury Regulation § 1.1091-1). Held more than a year, a gain or loss is long term (Topic 409).
• Germany. For securities held in collective custody, the ones bought first are deemed sold first (§ 20 Abs. 4 Satz 7 EStG), each amount converted at the exchange rate of its own date.
• India. Shares held in a demat account are matched first in, first out. The FIFO capital gains calculator also applies India’s tax rules: holding periods, grandfathering and the gains by category.
• Other markets. Choose the method your tax rules use: first in, first out, or the average cost of all your identical shares, worked out again at each purchase (the shares sold leave the pool at that average). Check your tax authority’s rule before you use the result.

Reading the results

• Each sale lists the purchases it was matched to and the rule that matched them, so you can follow the calculation line by line against your broker’s statement.
• Proceeds are the shares × the sale price; costs of sale are the commission and fees; the allowable cost is what the matched shares cost, with the fees paid to buy them.
• A wash sale or superficial loss keeps the loss out of this year: the amount is shown, and so is the purchase it was added to, which carries it until those shares are sold.
• The holding after each trade shows the shares and their cost (the Section 104 pool in the UK, the total ACB in Canada, the open lots elsewhere).
• Totals by tax year use the UK’s 6 April to 5 April year, India’s 1 April to 31 March year and the calendar year elsewhere; under “other markets” you choose the day your tax year starts (Australia’s income year starts on 1 July).

What it leaves out

The tax itself (each country’s calculator works that out from these figures), allowances and exemptions, crypto assets (their rules differ in places), shares from employee share schemes, gifts and inheritances, and corporate actions other than splits and consolidations (enter rights issues and demergers as purchases or adjustments with your own figures). Short sales are not handled: a sale larger than your holding is flagged. The rules look at every account you hold (and, for wash sales, your spouse’s and your retirement accounts): the tool sees only the trades you load.

Limitations

• One rule at a time: choose the country whose rules apply to you.
• Splits and consolidations are entered as adjustments; other corporate actions need your own figures.
• Short sales are not handled: a sale above your holding is an error, except in the UK, where HMRC’s last rule matches the extra shares with later purchases and the page says so.
• Not for crypto assets, options or employee share schemes.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.