SEIS and EIS Tax Relief Calculator

Undo Capital

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September 14, 2026

Startup Tax & Finance

Key takeaways

Your tax bill can cap the upfront claim. A headline rate alone does not show the sum you can use.
Loss relief applies to the allowable loss. You must first deduct sale proceeds and Income Tax relief.
SEIS can exempt half of a reinvested gain. EIS defers a gain, so the tax can return later.

Use this EIS tax relief calculator and SEIS tax relief calculator for an illustrative 2026/27 estimate. It covers upfront Income Tax relief, net investment cost, potential loss relief and capital gains treatment. Enter your investment, tax liability, tax rate and sale proceeds. The result is an estimate, not tax or investment advice.

How the SEIS and EIS tax relief calculator works

The Seed Enterprise Investment Scheme gives 50% relief on up to £200,000 a year. The Enterprise Investment Scheme gives 30% on £1 million. Its limit rises to £2 million where at least £1 million goes into a knowledge-intensive company. See HM Revenue & Customs (HMRC).

The marginal Income Tax rate drives the loss estimate, not the fixed 50% or 30% rate. The EIS calculator accepts UK bands and a custom Scottish rate.

See calculation

Qualifying subscription = lower of the investment and unused annual limit
Theoretical relief = qualifying subscription × 50% for SEIS, or × 30% for EIS
Claimable relief = lower of theoretical relief and available UK Income Tax liability
Net investment cost = investment − claimable upfront relief
Allowable loss = investment − sale proceeds − attributable Income Tax relief
Potential loss relief = allowable loss × marginal Income Tax rate
Effective net loss = investment − sale proceeds − upfront relief − loss relief

The EIS tax calculator must show each value. The EIS calculation starts with the allowable loss, not the investment. HMRC confirms the rule in its 2026 Share Loss Relief helpsheet.

SEIS / EIS Tax Relief Calculator · UndoCapital

SEIS & EIS tax relief calculator

See what an investment really costs you after income tax relief, and what you keep if the company fails or exits.

Step 1

Which scheme is the round under?

SEIS is for the earliest-stage companies. EIS follows once a company is past those limits.

Step 2

How much are you investing?

Relief applies to the first £200,000 you invest under SEIS in a tax year.

£0£200,000

Step 3

What is your income tax rate?

Relief can only reduce tax you actually owe, and it sets the value of loss relief later.

Your net cost after income tax relief

£12,500

for a £25,000 stake. 50% comes straight off your tax bill

Income tax relief

£12,500

Worst case you lose

£7,500

Income tax relief £12,500 Loss relief if it fails £5,000 Truly at risk £7,500

What you walk away with

Return on your net cost, after relief and with no CGT on the gain

Company fails

−£7,500

30% of the money you put in, once relief and loss relief are claimed.

Exits at 3×

+£62,500

£75,000 back, tax free, against £12,500 of net cost.

Exits at 10×

+£237,500

£250,000 back, tax free, against £12,500 of net cost.

Line by line SEIS · 50%

Investment £25,000

Income tax relief claimed −£12,500

Net cost to you £12,500

Loss relief if the company fails −£5,000

CGT saved on a 3× exit (24% rate) £12,000

CGT reinvestment relief available £12,500

Hold the shares for at least three years to keep the relief. SEIS also lets you reinvest a capital gain and exempt 50% of it, up to the amount you invest.

Illustration only, based on 2025/26 UK rates. Relief depends on your own tax position and the company qualifying. This is not tax advice.

Track SEIS/EIS in Undo →

SEIS vs EIS tax relief at a glance

The table shows core EIS and SEIS tax relief rules. These SEIS tax benefits apply only to qualifying subscriptions. Shares remain risky. Read Undo Capital's SEIS vs EIS guide.

Feature	SEIS	EIS
Upfront income tax relief	50%	30%
Annual investor limit	£200,000	£1 million, or £2 million with the KIC condition
Loss relief	Potentially available	Potentially available
Gain on qualifying shares	Potential disposal relief	Potential disposal relief
Relief for another capital gain	50% reinvestment relief	Deferral relief
General holding period	At least three years	At least three years

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Source: HMRC's investor guidance. Every EIS and SEIS tax relief estimate depends on the investor, company and qualifying shares. The EIS benefit calculator and EIS relief calculator must state that limit.

How capital gains treatment differs

SEIS reinvestment relief can exempt 50% of an eligible gain put into SEIS shares, up to £100,000. This SEIS capital gains tax relief needs Income Tax relief on the same subscription. See HMRC's HS393.

EIS can defer a gain invested from one year before to three years after disposal. The tax can return after disposal, redemption, loss of scheme status or a move abroad. The 2026/27 CGT rates are 18% and 24%. See HMRC's current rates.

Quick capital gains examples

On a £20,000 eligible gain, SEIS can exempt £10,000. At 24%, this is £2,400.
EIS can defer £4,800 of tax at 24%. The tax is not erased.

An EIS calculator UK needs a capital gains panel. A plain EIS tax calculator can overstate value if it calls deferral a saving. The SEIS investment tax relief view must split reinvestment relief from disposal relief.

SEIS and EIS tax relief examples

Both cases assume full eligibility, enough UK Income Tax liability and no sale proceeds. HMRC lets an eligible share loss, net of Income Tax relief, reduce income for the loss year or prior year. See HS286.

SEIS tax relief example: £10,000 investment

This SEIS tax relief example uses a 45% rate. The upfront claim is £5,000. The allowable loss is £5,000. Potential SEIS loss relief is £2,250. The net loss is £2,750.

Calculation	Result
Investment	£10,000
Upfront relief at 50%	£5,000
Allowable loss	£5,000
Loss relief at 45%	£2,250
Effective net loss	£2,750

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The seis tax relief calculator must show its assumptions. With only £3,000 of available tax liability, the £5,000 theoretical claim falls to £3,000.

EIS loss relief calculation: £10,000 investment

The EIS claim is £3,000. The allowable loss is £7,000. Relief at 45% is £3,150. The net loss is £3,850. An EIS loss relief calculator must use £7,000, not £10,000.

Calculation	Result
Investment	£10,000
Upfront relief at 30%	£3,000
Allowable loss	£7,000
Loss relief at 45%	£3,150
Effective net loss	£3,850

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At £4,000 of sale proceeds, the allowable loss is £3,000. Actual EIS loss relief rests on the claim route and tax position. Undo Capital's loss relief guide explains the concept.

What the calculator does not guarantee?

A result does not prove eligibility. Investors need an SEIS3, EIS3 or EIS5 before a claim. HMRC tests investor conditions. Shares must be new, fully paid and carry real risk. The three-year holding period still applies. Breaches can cut relief. See HMRC's current investor guidance.

Advance Assurance is an early view based on supplied facts. It is not an HMRC endorsement or a promise of relief. Founders still need the later SEIS/EIS compliance process.

Founders: help investors claim SEIS/EIS relief

A calculation can start an investor talk. Check the company, trade, cap table, use of funds and share rights. Then issue the right shares and complete the filings.

Undo Capital helps UK founders check scheme fit, prepare an Advance Assurance pack and manage records. Start with its Advance Assurance service, or check the Undo Capital glossary. Place this after the result.

FAQs

How much tax relief can I claim with SEIS or EIS?

SEIS offers 50%, and EIS offers 30% on eligible subscriptions. Annual caps are £200,000 and £1 million. EIS rises to £2 million under the knowledge-intensive condition. Relief cannot exceed your UK Income Tax liability. Treat the SEIS investment tax relief or EIS benefit calculator result as an illustration. HMRC confirms the limits.

How is SEIS or EIS loss relief calculated?

Deduct sale proceeds and attributable Income Tax relief from the investment. The result is the allowable loss. A claim against income uses the investor's tax position. The SEIS loss relief and EIS result can differ, since the upfront rates differ. An EIS loss relief calculator should show this working.

Is profit on SEIS or EIS shares free from Capital Gains Tax?

It can be, once disposal relief conditions are met. The investor must retain Income Tax relief and hold the shares for the required period, often three years. This differs from SEIS capital gains tax relief on another gain and from EIS deferral. See HMRC's SEIS disposal rules.

Can I carry SEIS or EIS relief back to the previous tax year?

Yes. Eligible shares can be treated as issued in the prior tax year, subject to its limit and available liability. Unused relief cannot move forward. Each year's rules still apply. The EIS calculator and EIS relief calculator need a carry-back note. HMRC covers EIS carry-back in HS341.

Do I need an SEIS3 or EIS3 certificate to claim tax relief?

Yes. You need the certificate before a claim. Investor rules still apply. The company submits SEIS1 or EIS1 first. HMRC then lets it issue SEIS3 or EIS3. Some approved fund investors get EIS5. Read Undo Capital's post-approval guide. The EIS calculator UK result cannot replace it.

References

Disclosure Notice: This communication is issued by Undo Capital Limited (“Undo Capital”) and is provided strictly for informational purposes only. It contains general information and should not be relied upon as accounting, business, financial, investment, legal, tax, or other professional advice. Undo Capital is not regulated by the Financial Conduct Authority (FCA) and does not provide investment, financial, or tax advice. Our services are designed to assist startups and businesses with company formation, legal agreements, and funding-related documentation. Nothing in this communication constitutes, or should be construed as, a recommendation, offer, or solicitation to purchase or sell any security or financial instrument.
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Participation in startups and early-stage enterprises involves significant risk. Such investments may be illiquid, may not generate dividends, may be subject to dilution, and may result in the total loss of invested capital. Any decisions or actions that may affect your business or personal interests should be taken only after seeking advice from suitably qualified professional advisors, and should form part of a balanced and diversified portfolio. This communication may contain links to third-party websites. The inclusion of such links does not imply endorsement, approval, investigation, or verification by Undo Capital. We accept no responsibility or liability for the content, accuracy, or use of information contained on any third-party websites.

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