How it's calculated
The Seed Enterprise Investment Scheme (SEIS) and the Enterprise Investment Scheme (EIS) give income tax relief to people who buy new shares in small, young, unlisted UK companies. For 2026/27, SEIS relief is 50% on up to £200,000 a tax year and EIS relief is 30% on up to £1 million, or £2 million if at least £1 million goes into knowledge-intensive companies.HM Revenue & Customs The relief reduces your income tax bill directly, but cannot reduce it below zero.
If the company fails, loss relief lets you set the loss, after the income tax relief already received, against your income at your marginal rate. Capital Gains Tax relief also applies: SEIS exempts half of a gain you reinvest, and EIS defers a reinvested gain until you sell the shares. The calculator uses 2026/27 CGT rates of 18% and 24%.HM Revenue & Customs
The formula
- Income tax relief = min(amount, annual limit) × 50% (SEIS) or 30% (EIS), no more than your income tax bill
- Net cost = amount − income tax relief
- Loss relief if the shares become worthless = net cost × your marginal income tax rate
- Most you could lose = net cost − loss relief (− any SEIS reinvestment relief)
- SEIS reinvestment relief = 50% of the gain reinvested (up to the investment) × your CGT rate. EIS deferral = the reinvested gain × CGT rate, payable later.
Worked example
An additional-rate taxpayer putting £100,000 into SEIS shares gets £50,000 of income tax relief, so the investment costs £50,000. If the company fails, loss relief at 45% is worth £22,500, leaving a worst-case loss of £27,500.
| Line | Amount |
|---|---|
| Amount invested | £100,000 |
| Income tax relief (50%) | -£50,000 |
| Net cost after relief | £50,000 |
| If the shares become worthless: loss relief at 45% | -£22,500 |
| Most you could lose | £27,500 |
The same £100,000 in EIS gets £30,000 of relief, with a worst-case loss of £38,500.
Assumptions and limitations
- The company and shares must qualify, and you need the company's compliance certificate to claim. Relief is withdrawn if you sell within three years or receive value from the company.
- Carry-back is not modelled. You can treat an investment as made in the previous tax year, which can help if that year's tax bill was higher.
- Loss relief at one marginal rate. A large loss can span tax bands; the calculator applies the rate you choose to all of it.
- Venture capital trusts have different rules (20% relief from April 2026) and are not covered.