Do not calculate the same shares independently at each broker. HMRC’s matching rules apply to the investor’s transactions in that security, so a purchase at Broker B can match a disposal at Broker A.
Simple cross-broker example
If you sell 100 shares on 1 June at one broker and buy 100 of the same class on 10 June at another, the later purchase can be a 30-day match. Separate broker calculations may incorrectly leave both transactions in their local Section 104 pools.
Security identity matters
Ticker symbols can differ by venue or change over time. Prefer stable identifiers such as ISIN where available, then review ambiguous matches. Similar fund names are not proof that two holdings are the same security.
HMRC's HS284 share-identification guidance applies by shares of the same class in the same company. Broker account boundaries do not appear in that matching order, which is why calculation-by-statement can miss cross-account matches.
Reconcile each source before relying on the combined result
| Check | Why it matters |
|---|---|
| Opening holdings and pooled cost | A current-year export may omit the acquisitions that created the cost basis. |
| Transaction count by broker | Detects skipped pages, duplicate files and unsupported rows. |
| Gross disposal proceeds | Supports the Self Assessment reporting test and report totals. |
| Fees and currency conversion | Small per-trade differences can accumulate across a large history. |
| Transfers between accounts | A transfer is not normally a disposal merely because one broker shows an outgoing row. |
A defensible workflow
- Export complete transaction history from each broker.
- Import and normalise all accounts before calculating.
- Resolve security-identity warnings.
- Reconcile transaction counts and proceeds to each statement.
- Inspect disposal matches and closing pool balances.
Start with the multi-broker calculator or read the methodology.
Owner and account scope still matter
Combine accounts only where the same beneficial owner holds the relevant securities. Do not merge another person's individual portfolio into yours merely because you share a household. ISA and pension activity also needs to be distinguished from a taxable investment account. Record ownership and wrapper type before resolving instrument identity.
Check the combined closing position
After matching, compare each calculated closing quantity with the sum of the taxable-account holdings shown by all brokers at the same date. Then inspect the closing pooled cost and average cost per unit for large or unexplained movements. A quantity mismatch often points to a missing transfer, split, duplicate export or omitted purchase; a cost mismatch can indicate fees, currency conversion or incomplete older history.
Document legitimate differences rather than forcing the calculator to equal a broker valuation. Broker market values are not Section 104 costs. The objective is a traceable bridge from imported transactions to the tax pool, with unresolved differences visible for review.
Official UK tax references
This guide is checked against published GOV.UK and HMRC material. FiscalFox is a calculation tool, not personal tax advice; review unusual transactions with a qualified adviser.