The EIS & SEIS calculator that shows the downside too.
Most calculators show the relief. This one puts every effect side by side with the same investment unsheltered - this investment's own journey, the CGT on gains from your other assets, even inheritance tax - each number broken down so you can see how it is built. Every rule is linked to the official record below.
e.g. from selling a property or shares - unrelated to this startup.
This investment.
what the scheme does to the money you put into this startup| With the scheme | Without | |
|---|---|---|
Relief, now a direct cut to your income tax bill | +£3,000
| £0
|
If it fails total loss of the company | −£3,850
| −£10,000
|
If it exits at 3× after the 3-year holding period | +£33,000
| +£25,200
|
£7,800 better if it works. £6,150 less lost if it fails.
Gains on your other assets.
selling a property or shares at a profit, unrelated to this startup - funding the investment with that gain changes its CGT| With the scheme | Without | |
|---|---|---|
A £10,000 gain elsewhere qualifies if the gain arose up to 36 months before or 12 months after this investment | £2,400 deferred
| −£2,400
|
£2,400 of CGT postponed until you choose to realise it.
Inheritance tax.
conditional - only if these shares are in your taxable estate; not added to the totals| With the scheme | Without | |
|---|---|---|
If it applies Business Relief, unquoted shares held at death | up to +£4,000
| −£4,000
|
Up to £4,000 of IHT avoided, if it applies.
All in at 3×: £23,000 profit with EIS, £15,200 without. If it fails: lose £3,850, not £10,000. That is what EIS is worth here.
Hold until 11 Sept 2029 (earlier disposal claws back relief) · claim by 31 Jan 2033 once your EIS3 certificate arrives · assumes this tax year · sufficient tax liability assumed · CGT at 18%/24%, annual exempt amount ignored · IHT assumes a taxable estate · information, not tax advice.
How the relief actually works - a worked example
One investment, followed step by step: £10,000 into an EIS-qualifying company, by a 45% taxpayer. (SEIS works the same way with 50% relief and a £200,000 annual cap.)
- 1You invest £10,000
The company must hold, or obtain, EIS qualification - most raises get HMRC advance assurance first, and you should ask to see it.
- 2£3,000 comes back
30% income-tax relief, claimed with the EIS3 certificate the company sends after completing the raise. It reduces your income-tax bill, not your taxable income.
- 3Your real exposure is £7,000
The relief means only 70% of the cheque is ever at risk - and less than that once loss relief is counted.
- 4If it fails: lose £3,850, not £10,000
Loss relief lets you set the £7,000 at-risk amount against income at your marginal rate: 45% of £7,000 is another £3,150 back.
- 5If it works: the gain is tax-free
Hold for three years and claim the relief, and there is no capital gains tax on exit. Sell earlier and the relief is clawed back.
The full mechanics, including the 2026 rule changes and the reliefs on gains from your other assets: EIS & SEIS rules in 2026 · the downside maths · the glossary.
Every relief, in one place
EIS and SEIS are not one tax benefit but a stack of six. The calculator above computes the first five; the sixth depends on your estate, so we state the rule rather than guess your number.
EIS 30% · SEIS 50% of the amount subscribed, against this year's income tax or carried back one year.
If the company fails, the net loss (after income tax relief) is deductible against income at your marginal rate - up to 45%.
No capital gains tax on the growth when you sell after the 3-year holding period.
Tax on gains made up to 36 months before or 12 months after the investment is deferred while you hold - and can be re-deferred.
Half of a gain reinvested into SEIS shares is permanently exempt - the tax never returns, even if the company fails.
Unquoted EIS/SEIS shares usually qualify for Business Relief: 100% IHT relief after 2 years if still held at death. From 6 April 2026 the 100% rate applies up to the government's per-estate allowance for business and agricultural property (announced at £2.5m), with 50% relief above it.
Checked against the official records
Nothing here is invented: each figure the calculator produces is arithmetic on rules published by HMRC and GOV.UK. The sources, so you can verify every number yourself:
Rules as published at the time of writing; reliefs depend on your circumstances and on the company keeping its qualifying status. Tero is software. We are not a fund, we do not hold client money, and we do not provide investment, tax or legal advice. Information, not tax advice. Capital at risk.