By the time filing season arrives, the problem is rarely that you have no data; it is that every investment platform tells only part of your tax story.
Your broker may report a realised profit, a crypto exchange may produce its own trading summary and a self-custody wallet may provide no tax figure at all. Each record can be accurate within its own boundaries and still fail to answer the question that matters for your Self Assessment: what is your complete UK tax position for the year?
Finbooks brings those fragments into a single calculation across your traditional investments and crypto. Rather than treating platform totals as tax figures, it works from the underlying transactions, applies the relevant UK treatment to gains and income, preserves the costs, losses and allowances that affect the result, converts the required amounts into pounds and prepares the figures for Self Assessment.
Bringing the full investment tax history together protects you in both directions, preventing taxable income and disposals from slipping through while preserving the costs, losses and allowances that can reduce your bill. That balance is the starting point for paying the right amount of tax.
What does paying the right amount of investment tax mean?
Paying the right amount of investment tax is not simply a matter of correcting the numbers when Self Assessment is due. It begins with holding investments in the appropriate accounts, using tax wrappers such as ISAs and pensions where they suit the investor's objectives, and understanding when a disposal will bring a gain or loss into a particular tax year. Once transactions have taken place, the calculation must include every taxable gain and source of income without losing the acquisition costs, capital losses, allowances and reliefs that legitimately reduce the bill.
Tax efficiency and tax accuracy are therefore part of the same exercise. An investor may be able to shelter future returns inside an ISA, use realised losses against gains or choose the timing of a disposal when there is genuine flexibility, but none of those decisions removes the need to report what has already become taxable. The aim is to avoid paying more tax through missed allowances or losses without creating an underpayment by overlooking income, disposals or HMRC's matching rules.
There is also a cash-flow issue that platform profit figures rarely reveal. Self-directed brokers and crypto exchanges execute transactions and provide account records, but they cannot see the investor's full portfolio, tax band or activity elsewhere, and they do not normally reserve cash against the investor's final UK liability. Sale proceeds can be reinvested immediately, a dividend can be automatically reinvested and a crypto-to-crypto swap can create tax without producing any sterling at all, leaving the investor to fund the eventual Self Assessment bill from other cash if nothing was set aside.
Finbooks turns that scattered history into a tax position you can act on before the filing deadline. Gains and income sit alongside the costs, losses and allowances that change the bill, so you can understand what may be due, trace it back to the underlying transactions and keep enough cash available rather than discovering the liability after everything has been reinvested.
Taken together, those are the three parts of paying the right amount: making tax-efficient decisions before a transaction, calculating the consequences correctly afterwards and keeping enough liquidity available for the bill. The practical work begins by establishing which accounts and assets belong inside the taxable calculation in the first place.
Which investments and accounts are taxable in the UK?
UK tax normally follows the investor's tax residence, not the location of the broker, exchange or wallet. A UK resident may need to report worldwide investment income and gains, subject to individual circumstances and any residence relief that applies.
The first step is to separate tax wrappers from taxable holdings, since investments that look similar on a portfolio dashboard can belong to entirely different tax environments.
Stocks & Shares ISAs and pensions
Eligible gains and income arising inside a Stocks & Shares ISA are generally free from UK Capital Gains Tax and Income Tax. For 2025/26, the ISA subscription allowance was £20,000 across all of an individual's ISAs. From a tax perspective, it therefore made sense to consider available ISA capacity before placing new eligible investments in a General Investment Account, provided the wrapper suited the investor's access needs and investment objectives. Any unused 2025/26 ISA allowance was lost after 5 April 2026 rather than carried into the next tax year.
Existing investments in a General Investment Account cannot normally be moved directly into an ISA. A Bed and ISA usually involves selling the investment outside the wrapper and buying it back inside, which means the sale remains a disposal for Capital Gains Tax and the repurchase uses the current year's ISA allowance. When changing ISA provider, using the formal ISA transfer process also avoids treating the move as a withdrawal followed by a new subscription.
Registered pensions provide another tax-efficient environment, although the headline allowance needs context. The standard pension annual allowance was £60,000 for most people in 2025/26 and covered pension inputs across their schemes, including employer contributions; it could be lower for high earners or anyone subject to the Money Purchase Annual Allowance. Ordinary investment activity inside the pension does not enter the investor's personal capital gains calculation, but contributions and eventual withdrawals follow their own pension tax rules.
Tax-wrapper protection works both ways: a loss arising inside an ISA or pension cannot normally be claimed against gains outside it, so wrapped activity must remain separate from taxable accounts. Direct cryptoassets cannot be held inside a Stocks & Shares ISA either; where an eligible listed product provides crypto-related exposure, the tax treatment follows that product rather than direct ownership of the underlying tokens.
General Investment Accounts and foreign brokers
Shares, ETFs, funds, bonds and derivatives held outside a tax wrapper may all need to be considered for Self Assessment, whether they are held with a UK or overseas broker. Sales can give rise to capital gains or losses, while dividends, bond interest and interest on cash are generally taxed as income.
Using an overseas broker does not remove the activity from UK tax; instead, it usually adds work around sterling conversion, foreign withholding tax and account statements that may follow a calendar year rather than the UK tax year.
Crypto exchanges and self-custody wallets
Crypto remains part of the UK tax position after it leaves an exchange. Moving tokens to a self-custody wallet normally changes where they are held, not who owns them, so the original acquisition history must follow the assets.
A private wallet can still include taxable disposals, swaps and income from staking or DeFi. Where no tax report is available, the wallet history needs to be reconstructed and reconciled with the related exchange activity to determine the correct UK tax treatment.
You invest. We handle the tax.
Which investment and crypto transactions can trigger tax?
Because tax follows the event rather than the withdrawal of money from a platform, the same investment may create a capital disposal, income or no immediate tax event at different points in its life.
Disposals that can create a capital gain or loss
Selling shares, funds or other chargeable investments can create a capital gain or allowable loss. Crypto disposals include selling tokens for pounds, exchanging one cryptoasset for another, spending crypto on goods or services and gifting it to someone other than a spouse or civil partner.
Because no fiat currency enters the transaction, a crypto-to-crypto swap is easy to overlook; for UK tax, however, it is normally a disposal of the token given up and an acquisition of the token received. Fund redemptions and the closing, exercise or expiry of some derivative positions can also require a capital gains calculation.
Investment and crypto income
Dividends, interest, bond coupons and fund distributions are income rather than capital gains, as can crypto received from employment, trading, mining, staking or providing a service. Airdrops and DeFi returns require more context because their treatment depends on why the tokens were received and the rights created by the arrangement.
When tokens are taxed as income on receipt, their sterling market value at that point generally contributes to the acquisition cost used for a later disposal. The tokens can therefore create an Income Tax amount when received and a separate Capital Gains Tax calculation when eventually sold or exchanged.
Buying, holding and moving your own assets
Buying an investment and continuing to hold it does not normally create a disposal. Unrealised gains are not taxed merely because the market value increased, and an open position does not become taxable because the profit appears on a dashboard.
Transfers between accounts or wallets owned by the same beneficial owner are not disposals, provided the original acquisition date and cost remain attached to the asset. If the two sides of a transfer are not connected, the tax history may lose that cost or mistake the movement for a sale.
But correct classification solves only half the problem: the calculation must also see every broker, exchange and wallet through which those events occurred.
Have you included every broker, exchange and wallet?
Leaving an account out of the calculation can change the cost basis of a disposal made elsewhere, hide investment income or leave a transfer looking like a taxable event, so the effect rarely remains confined to the missing account.
If shares bought through Interactive Brokers are later transferred and sold through Trading 212, the sale still depends on the earlier acquisition cost. Bitcoin that moves from an exchange into self-custody before being sold elsewhere follows the same principle: its token pool must retain every relevant acquisition and disposal throughout the route.
A complete review includes active and closed platforms, old wallets, transferred positions and accounts that generated income without any sales. Earlier tax years may also matter because an asset sold in 2025/26 can carry a pooled cost built up years before.
That is why Finbooks carries the history across platform boundaries: an acquisition made in one account can still inform a disposal in another, while activity from closed brokers or old wallets remains part of the same UK tax position.
Are your capital gains calculated under HMRC rules?
HMRC matches acquisitions and disposals in a fixed order, which means a platform can identify every trade correctly and still show the wrong cost basis if it cannot apply the UK rules across the investor's other accounts.
Same-day matching
An acquisition made on the same day as a disposal of the same asset is matched first, ahead of the older purchases already sitting in the Section 104 pool.
The 30-day rule
HMRC next matches acquisitions of the same asset made during the 30 days following the disposal. Because the rule applies across the investor's accounts, a sell-and-rebuy on different platforms can use the cost of the later purchase instead of the average cost shown by the selling platform.
Section 104 pooling
After same-day and 30-day matching, shares of the same class in the same company are generally held in a Section 104 pool with an average allowable cost. Crypto uses a similar pooling approach, with a separate pool for each type of token.
Each share class and token type keeps its own pool, so Bitcoin and Ether remain separate just as shares in two different companies do.
Fees, losses and transferred assets
Allowable acquisition and disposal costs can reduce the chargeable gain, including dealing commission, Stamp Duty Reserve Tax and qualifying crypto transaction or network fees where applicable. Properly claimed capital losses can reduce the tax due on gains in the year or be carried forward, helping to avoid unnecessary overpayment without changing what must be reported.
Have you separated capital gains from investment and crypto income?
The overall profit shown on a portfolio dashboard does not translate directly into a single taxable figure. Dividends are taxed under the dividend rules, interest and bond coupons fall within savings income, and gains from shares, funds and crypto disposals are subject to Capital Gains Tax.
Reinvesting a dividend does not change its treatment as income in the year it is received. The reinvestment is treated as a new acquisition with its own allowable cost.
Capital losses cannot be set against dividends, interest, staking income or other amounts taxed as income. They can only be used against chargeable capital gains, whether those gains arise from shares, crypto or another chargeable asset.
Have foreign investments and currencies been converted correctly?
Foreign shares, overseas dividends, multi-currency broker balances and crypto transactions quoted in dollars or stablecoins all need a sterling value for UK tax.
Sterling conversion takes place event by event, so a US share bought in dollars needs a sterling acquisition cost on the purchase date and sterling proceeds on the sale date, while crypto acquisitions, disposals and income quoted in dollars or stablecoins need their own date-specific pound values. Converting only the final platform profit can miss currency movements between those events.
Foreign dividends and interest are generally reported gross, before overseas withholding tax, with Foreign Tax Credit Relief considered separately where available so the same income is not taxed twice beyond the permitted amount.
Have you checked ETFs, funds and DeFi for income you did not receive in cash?
An offshore ETF's UK reporting fund status can change the treatment of a disposal, with gains on non-reporting offshore funds potentially taxed as income rather than as capital gains. Reporting funds can create a different issue by producing excess reportable income, including on accumulating share classes where nothing was distributed to the investor in cash.
DeFi activity can create taxable income or disposals without them being immediately obvious to the investor. Staking and lending rewards may be taxable as income, while depositing tokens into or withdrawing them from a protocol can amount to a disposal where beneficial ownership changes. The tax treatment depends on the rights transferred and the structure of the arrangement, rather than the terminology used by the protocol.
Can you trust broker statements and crypto tax reports?
Platform reports can provide detailed and accurate tax information, but they are generally built around the activity held on that specific platform, rather than the investor’s complete UK tax position. Different brokers and exchanges may also report data differently, for example using the calendar year, showing dividends net of withholding tax or calculating gains only from transactions recorded on their platform.
Even a complete specialist crypto tax report therefore covers only the crypto side of the picture. Shares sold elsewhere, dividends, interest, offshore funds and capital losses from other investments may all affect what ultimately needs to be reported through Self Assessment.
Finbooks is built around that distinction: traditional investments and crypto meet in one UK tax-year position, while their pools and tax treatments remain separate wherever the rules require it.
Once that investment history has been assembled and classified, the resulting gains and income can be tested against the allowances, rates and deadlines for the relevant tax year.
Which allowances and rates apply for 2025/26?
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026, and the figures below are the ones that apply to that period.
Capital gains
For individuals, the Capital Gains Tax annual exempt amount is £3,000, with gains above the available amount normally taxed at 18% to the extent they fall within the unused basic-rate band and at 24% above it.
Even when no Capital Gains Tax is due, the SA108 capital gains pages may still be required if you are already within Self Assessment and total disposal proceeds exceeded £50,000 during 2025/26.
Dividends
The dividend allowance for 2025/26 is £500, after which dividends are taxed at 8.75% within the basic-rate band, 33.75% within the higher-rate band and 39.35% within the additional-rate band.
Savings income
The Personal Savings Allowance is normally £1,000 for basic-rate taxpayers, £500 for higher-rate taxpayers and nil for additional-rate taxpayers.
Self Assessment dates
If you need to file for the first time, you generally need to tell HMRC by 5 October 2026. The usual deadline is then 31 October 2026 for a paper return and 31 January 2027 for an online Self Assessment return and any outstanding tax. If you make payments on account, remember that the second payment is due by 31 July.
With the correct year's figures in place, the remaining task is to turn the calculation into a repeatable pre-filing review.
How can you check your UK investment tax before filing?
A proper UK tax review starts by reconstructing the investor’s complete transaction history, rather than treating the final profit shown by a platform as the taxable result.
1. List every broker, exchange, wallet and taxable investment account used during or before the tax year.
2. Separate ISA and pension activity from taxable holdings.
3. Import complete histories, including earlier acquisitions and closed accounts.
4. Match transfers so they are not mistaken for disposals and retain their original cost.
5. Classify disposals, dividends, interest, staking, DeFi and other income separately.
6. Convert every relevant event into pounds at the correct date.
7. Apply same-day, 30-day and Section 104 pooling to each asset across platforms.
8. Apply allowable costs, capital losses, allowances and the correct tax rates.
9. Reconcile the result with broker statements, exchange records and available reporting data.
10. Investigate missing costs, unmatched transfers and unexplained balances before filing.
Those are the steps an investor like you would otherwise need to work through manually. Finbooks does that work across your complete investment history, applying the relevant UK tax rules and producing reconciled figures ready for Self Assessment.
What mistakes make UK investors pay the wrong amount of tax?
The mistakes that lead UK investors to pay the wrong amount of tax are often simple: missing transactions, using incomplete records, overlooking costs or losses, or applying the wrong tax treatment. Some leave tax unpaid and can lead to interest or penalties. Others mean paying HMRC more than you actually owe.
Common problems include:
reporting broker or exchange profit as if it were a UK tax figure;
forgetting closed accounts, old wallets or transferred assets;
using calendar-year statements for a 6 April to 5 April tax year;
missing crypto-to-crypto swaps or crypto spent on goods and services;
treating a transfer between your own accounts or wallets as a disposal;
omitting reinvested dividends, staking rewards or DeFi income;
converting only the final foreign-currency profit rather than each relevant event;
calculating every broker or exchange in isolation;
ignoring excess reportable income from an offshore fund;
failing to include allowable acquisition costs or claim capital losses.
What investment tax records should you keep for HMRC?
The figures reported on Self Assessment should be traceable back to dated transactions. Keep the original broker and exchange CSVs, account statements, contract notes, dividend records, evidence of foreign withholding tax and the exchange-rate sources used in the calculation.
For crypto, retain exchange histories, public wallet addresses, transaction hashes and evidence linking transfers between accounts you control. Records for missing platforms, token migrations and manually classified DeFi activity should explain how the final treatment was reached.
A PDF summary can support the calculation, but once a portfolio spans several platforms it cannot replace the underlying history needed to trace every sterling gain and income figure back to its source.
Check the right amount of UK investment tax with Finbooks
Once shares, funds and crypto are spread across platforms, paying the right amount requires more than adding their reports together. The calculation has to capture every taxable event without losing the costs, losses and allowances that reduce what you owe.
Finbooks works through your full investment history across brokers, exchanges and wallets, applying the relevant UK tax treatment to each transaction rather than relying on the final figures reported by each platform. Trades, disposals, dividends, interest, costs and losses are reconciled into Self Assessment-ready figures that can still be traced back to the original activity, checked and corrected before filing.
