Choosing the best Investment Platform for a GIA account (for HMRC tax reporting)

If you have used up your £20k ISA annual allowance, you may want to open a General Investment Account (GIA) and you need to be aware that these are taxable.

Choosing the right GIA platform is important because you cannot easily switch to another platform without triggering a Capital Gain and thus CGT if your gain is over £3k!

Each year you will need to consider the following points:

1. You are allowed £3k of gains before Capital Gains (CG) is due.
2. If you sell your shares, you need to calculate the Capital Gain (CG).
3. Gains are calculated according to three main HMRC rules: same day transactions, 30-day rule and the Section 104 averaging rule.
4. Because of these three rules, the annual report supplied by your broker platform is not suitable to directly use in your tax report. e.g. you cannot simply use the net gain/loss figure for the tax year.
5. If you have more than one GIA with different brokers, you should combine all trades before you work out the CG for tax purposes. This is because you may have purchased the same shares on one platform within 30 days of selling the same shares on a different platform and this will affect CG calculations due to the 30-day rule.

Another complication of using a GIA is that you also need to calculate income and dividends. Note that even if you hold an accumulating ETF, you may need to declare the dividends that it earned in the tax year even though the dividends were not paid out (see my ERI blog articles for details on this little known HMRC tax rule). Indeed, some distributing ETFs may also produce Excess Reportable Income in addition to the paid dividends (but usually in very small amounts) which also need to be declared as well as the paid dividends. Most investors prefer to hold distributing ETFs rather than accumulating ETFs within their GIA for this reason. If you are a Basic rate tax payer, you may be paying too much tax if you have accumulating ETFs in your GIA and don't account for ERI - if you are a higher rate tax payer, you may be paying too little tax and the tax man may be coming after you.

Fidelity (CGT report now includes ERI as of April 2025) and Invest Engine (ERI not included) report gains/losses according to HMRC rules (untested) but most Investment platforms do not provide a suitable CG report for use with HMRC. Fidelity has reasonable charges for largish accounts which are capped, but the charge per trade (£7.50) may become significant if you make lots of trades per year.

I have found these free tools which can calculate CG with HMRC rules from broker downloaded data.

• cgtcalculator.com - free online site which requires data in a specific format. Conversion tools are available for several popular broker platforms. Mature, widely used site for many years. Single .txt file can be uploaded or you can cut and paste cells from Excel. ERI is not accounted for. CG calc only (no dividends). Calculation workings are shown for each sell trade and so they can be manually checked.
• cgtcalc.co.uk UK Tax Calculator - very new online site which you can directly upload transaction files to and it will work out dividends, CG and ERI. The CG results seem to match (or very nearly match) the cgtcalculator.com results. I have not tested or examined the accuracy of Dividend and ERI results yet. It produces very nice PDF results with relevant HMRC tax form fields filled in. The PDFs could be attached to your self assessment submission. It also accepts text files in the same format as used for cgtcalculator.com.
• cgttaxtool.uk - (failed my testing - results were wildly wrong) - not sure if results are accurate. Reddit account appears to have been banned. No ERI support. Check results carefully!
• taxbull.co.uk - tested with T212 data. Roughly agrees with cgtcalculator.com but you may have to input stock splits manually. T212, Robinhood, Tastytrade, FreeTrade .csv files supported. Warns not to use for HMRC submissions due to same day and 30-day rule errors possible. Missing buys don't seem to be checked for, so make sure your csv files include all buys/sells over all years with no gaps. No ERI support.
• whatsmycgt.co.uk - requires single csv/xlsx in correct format which must be manually prepared using Excel (untested).

Note that you need to upload all CSVs for ALL dates/years (multiple .csv files can be uploaded at the same time by using ctrl-left-click). I suggest using and comparing CG results from the first two sites in the list above.

The table below may help you to decide which broker Platform to choose for your GIA account:

A blank fields means no calculator is known to exist. 'supported' means no conversion tool needed

The conversion tool for Interactive Investor CSVs on the cgtcalculator.com site does not cope with a nasty bug in ii CSV files (bug: price of foreign  $USD shares are denominated in £ not $USD, e.g. price £1.50 when the price was actually $1.50) but the conversion tool on my blog page works around this bug. It may mean that if you have an ii GIA, the cgtcalculator.com + my conversion tool is the only accurate way available as other online tools may not be aware of the bug in the ii CSV files! If you have not sold any non-£GBP shares on ii then you should have no problem with the other calculators.

The new UK Tax Calculator site also accepts .txt text files which are in the cgtcalculator.com text format, so the same cgtcalculator.com conversion tool can be used to convert your downloaded .csv files into the correct format .txt file.

Trading 212 and Interactive Brokers seem to be the best choices if you have a GIA and want easy CGT calculations (because they csv's can be imported directly into UK tax Calculator and also double-checked on cgtcalculator.com). If you only deal with Fidelity, then their report is HMRC ready anyway, with CG and ERI included and so Fidelity tax reporting should be painless. If you are an eToro club member, they provide an HMRC compatible tax report (ERI is not mentioned though).

Pro-tip: If you are holding accumulating ETFs, the most reliable way to find your ERI figures for each holding is to search the KPMG Offshore Reporting Funds portal using the ISIN number of the fund (free login sign up required) - OR - find the specific fund manager's website (e.g. Vanguard, Van Eck or iShares, etc.) and look for their "Report to Participants" reports. ERI only applies if you held the fund on the Reporting Date of the fund.

An alternative to cgtcalculator.com is WhatsMyCGT.co.uk which can be used for HMRC reporting (but check it with accountant) and it says it includes ERI reporting too. I have not yet tested it. No conversion tools seem to be available, so you must use Excel to manually prepare the data in the correct format. Note that UK ticker symbols are sometimes mis-interpreted and so the ERI may be wrong if shares are incorrectly identified. ISIN numbers are much more accurate than ticker symbols.

Whatsmycgt.co.uk format

cgtcalculator.com format (paste data cells only, omit headings row)

Tools like WhatsMyCGT and cgtcalculator are especially useful for share pooling calculations (when you have more than one broker/GIA account). All prices must be in £GBP. If any prices in the .csv file are in $USD (for example) then you will need to find the exchange rate for that buy or sell date and convert it to £GBP! If the total net amount is in £GBP (net of platform, tax and Fx charges) then you can divide the net amount by the number of shares to get a 'net' share price and set Charges and Tax and Brokerage columns to 0.

If you have a correction or anything else to add to this article, please contact me.

cheers

Steve