cgt calculator shares

How this CGT calculator for shares works

This tool estimates tax on a single share disposal. It starts with your sale proceeds, subtracts allowable acquisition and selling costs, and then applies losses and annual allowance before calculating tax at your chosen rate.

It is built for practical planning: quick scenario testing before you place a trade, so you can estimate the tax impact of selling now versus later.

Calculation formula

Step 1: Work out disposal proceeds

Disposal proceeds = (shares sold × sale price per share) − selling fees

Step 2: Work out acquisition cost

Acquisition cost = (shares sold × buy price per share) + purchase fees

Step 3: Find the gain

Raw gain = disposal proceeds − acquisition cost

Step 4: Apply losses and allowance

Net gain after losses = raw gain − losses brought forward
Taxable gain = max(0, net gain after losses − annual CGT allowance)

Step 5: Estimate tax due

Estimated CGT = taxable gain × CGT rate

Important notes for share investors

• This is an estimate and not personal tax advice.
• Real tax treatment may depend on local rules, tax residency, and account type.
• Tax-sheltered accounts (for example ISA/Roth-style wrappers) may be exempt from CGT depending on jurisdiction.
• In some countries, share matching rules (same-day, 30-day, pooled holdings) can alter your effective cost basis.
• Corporate actions such as stock splits, rights issues, and spin-offs can affect cost calculations.

Worked example

Suppose you sell 1,000 shares at £4.20 that you bought at £2.50. You paid £25 in purchase fees and £20 in selling fees.

• Disposal proceeds: 1,000 × 4.20 − 20 = £4,180
• Acquisition cost: 1,000 × 2.50 + 25 = £2,525
• Raw gain: £4,180 − £2,525 = £1,655
• If your annual allowance is £3,000, taxable gain is £0
• Estimated CGT: £0

If your gains exceed allowance, the calculator will show the taxable portion and tax estimate at your selected rate.

Ways to reduce share CGT legally

1) Use annual allowances efficiently

Consider staging disposals across tax years if it helps you use allowances more effectively.

2) Offset capital losses

Realized losses can reduce taxable gains. Keep records and report losses where required.

3) Review account structure

Holding investments in tax-advantaged wrappers can materially change long-term tax outcomes.

4) Keep excellent records

Store contract notes, fees, and corporate action adjustments. Good records reduce errors and stress at filing time.

Final thought

A CGT calculator for shares helps you make better sell decisions with fewer surprises. Use it as a planning tool, then confirm details against current tax rules (or a qualified adviser) before filing.