UK SEIS: Seed Enterprise Investment Scheme Guide for 2026

Investing in early-stage startups is high risk -- but the UK government has designed a scheme that dramatically improves the odds for investors willing to back them. The Seed Enterprise Investment Scheme (SEIS) offers up to 50% income tax relief, Capital Gains Tax exemption, and meaningful loss protection. Here is how it works in 2026 and who it suits.

What Is SEIS?

SEIS is a government-backed scheme designed to encourage private individuals to invest in very early-stage UK businesses. In return for putting money into a qualifying startup, investors receive generous tax reliefs that reduce the effective cost and risk of the investment.

The scheme was first introduced in 2012 and has been significantly expanded over the years. From April 2023, the investor limit was raised to GBP 200,000 per tax year (up from GBP 100,000), making it more attractive for higher-net-worth investors.

SEIS sits alongside the older Enterprise Investment Scheme (EIS), which targets slightly more established companies with larger funding requirements. SEIS is specifically for seed-stage companies -- the earliest and riskiest investments.

The Core Tax Reliefs

1. Income Tax Relief: 50%

This is the headline benefit. If you invest GBP 20,000 in a SEIS-qualifying company, you can claim GBP 10,000 off your income tax bill. The relief is claimed through Self Assessment and reduces the tax you owe for that year (or the previous year if you carry it back).

Important: The relief is capped at the amount of income tax you actually owe. If you invest GBP 20,000 but only owe GBP 7,000 in income tax, your relief is limited to GBP 7,000.

2. Capital Gains Tax Exemption

If you hold your SEIS shares for at least three years and the company is still qualifying at the point of disposal, any profit you make on selling the shares is entirely free from Capital Gains Tax. Given standard CGT rates of 18% or 24%, this can be extremely valuable if the startup succeeds.

3. CGT Reinvestment Relief

If you have realised capital gains elsewhere -- for example from selling property or shares -- you can use a SEIS investment to shelter up to 50% of those gains from CGT. This is in addition to the income tax relief, making SEIS one of the few investments that can attract two forms of tax relief simultaneously.

4. Loss Relief

SEIS investments can and do fail. If they do, you can claim loss relief on the effective loss -- the amount you invested minus the income tax relief already received. This loss can be offset against income tax at your marginal rate.

Example: You invest GBP 10,000. You receive GBP 5,000 income tax relief. The company fails and the shares are worth zero. Your effective loss is GBP 5,000. If you are a 40% taxpayer, you can claim a further GBP 2,000 in loss relief. Your total tax benefits: GBP 7,000 on a GBP 10,000 investment -- meaning your maximum downside is just GBP 3,000.

What Companies Qualify?

For a company to be SEIS-eligible, it must:

• Be incorporated in the UK
• Not be listed on a recognised stock exchange (unquoted)
• Have been carrying out a qualifying trade for no more than three years
• Have fewer than 25 full-time equivalent employees
• Have gross assets of no more than GBP 350,000 at the time of investment
• Raise no more than GBP 250,000 in total SEIS investment (lifetime limit)

Excluded sectors include: property development, financial services (banking, insurance, money-lending), legal or accountancy services, farming, forestry, and operating or managing hotels and nursing homes.

Companies must obtain advance assurance from HMRC before issuing SEIS shares, giving investors confidence that the company and investment are eligible.

What Are the Investor Rules?

To claim SEIS relief, you must:

• Be a UK taxpayer with sufficient income tax liability to absorb the relief
• Not be connected to the company (broadly: not a paid employee or director before the shares are issued, and not owning more than 30% of the company)
• Hold the shares for at least three years

You can be an employee of the company after the investment is made -- this is a key difference from EIS, where employees are generally excluded.

Carry Back Relief

One of SEIS's more powerful features is the ability to carry back. If you invest in the 2026/27 tax year, you can treat some or all of that investment as having been made in 2025/26 instead. This is useful if your income was higher in the prior year, or if you want to accelerate your tax refund.

Carry back is limited to the SEIS investment limit for the earlier year and you must make the election on your Self Assessment return.

How to Invest in SEIS

You have several routes:

• Direct investment: Contact SEIS-eligible companies directly and negotiate an investment. Requires your own due diligence.
• SEIS funds: Specialist fund managers pool investor money across a portfolio of SEIS companies, spreading risk. You still receive the full 50% relief.
• Crowdfunding platforms: Some regulated crowdfunding platforms list SEIS-qualifying deals, making it easier to find and invest in early-stage companies.

Always check that the company has HMRC advance assurance and will issue you a compliance certificate (SEIS3) after the investment is completed. You need this certificate to claim the relief on your Self Assessment return.

SEIS vs EIS: Which Is Right for You?

If you want the highest tax relief and are willing to accept the greater risk of very early-stage companies, SEIS is the better choice. EIS suits slightly later-stage companies and larger investment amounts.

---

SEIS tax relief reduces how much income tax you owe -- but understanding your full tax position is essential before committing funds. Use the CalcHub take-home pay calculator to model your annual income tax liability and work out exactly how much SEIS relief you could realistically claim against your bill.