Tools
The SEIS calculator.
Put a number in, see what the scheme does to it: the income tax relief up front, the real cost if the company fails, and what a gain on the way in changes. Every figure follows the current rules, and none of it is advice.
Your numbers
The exit is your hypothetical, not our forecast. Most early companies fail; the risks guide is one click away.
And the honest bit
And if it fails completely: with SEIS the true loss is £3,000, 30p of every pound invested; without it, the full £10,000 is exposed before any capital loss claim.
Bars compare net cost today against after-tax value at your hypothetical exit. Assumes qualifying shares held three years, enough income tax liability to use the relief, and ignores the CGT annual allowance. Education, not advice.
The same money, with and without SEIS
| SEIS | Without | |
|---|---|---|
| Income tax relief | £5,000 | £0 |
| CGT relieved on entry | £0 | £0 |
| Net cost today | £5,000 | £10,000 |
| After-tax value at your exit | £30,000 | £25,200 |
What the numbers mean
Income tax relief is a deduction from your tax bill, not from taxable income: invest £10,000 and £5,000 comes off what you owe, this year or carried back to last year. It needs enough liability to absorb it, and it is capped at £200,000 of subscriptions per tax year. The full mechanics, including carry back, live in the 50% explained.
The failure line uses loss relief: if the company fails, your loss after the upfront relief can be set against income at your marginal rate. At 45%, a total failure costs 27.5p in the pound; at 40%, 30p; at 20%, 40p. The worked arithmetic is in the loss relief guide.
Reinvestment relief matters only if you fund the investment from another gain: half of the matched gain becomes exempt from CGT permanently. It is an exemption, not a deferral, which is what makes it unusual. Detail in the CGT reliefs guide.
Disposal relief is the quiet fourth relief: hold qualifying shares three years and the growth is CGT-free on exit, which is what the exit comparison shows. What happens on the way out, door by door, is in the exit guide.
Whether the whole package is right for anyone is a different question from what the arithmetic says: is SEIS worth it takes that question seriously.
Common questions
Is this SEIS calculator accurate?
It applies the current rules exactly: 50% income tax relief up to £200,000 per year, loss relief at your marginal rate on the net loss, 50% reinvestment relief on matched gains, and CGT-free disposal after three years. What it cannot know is your personal position, which decides how much of each relief you can actually use.
Does the calculator store my numbers?
No. It runs entirely in your browser and sends nothing to us or anyone else.
What can remove these reliefs?
Selling inside three years, the company losing SEIS status, receiving value back from the company, or not having the tax liability the relief needs. The risks guide covers each one honestly.
How does SEIS tax relief work?
Invest in a qualifying company and 50% of the amount comes off your income tax bill, up to £200,000 of subscriptions per tax year. Behind that headline sit three more reliefs: reinvestment relief on the way in, tax-free growth on the way out, and loss relief underneath. The full guide walks all four.
How much can you invest in SEIS each year?
Relief is available on up to £200,000 of SEIS subscriptions per tax year. You can invest more, but the excess earns no relief, which is why the SEIS calculator caps its input there. Carry back can effectively double a first year by using last year’s unused capacity too.
How is SEIS loss relief calculated?
Take what you invested, subtract the 50% relief you already received, and multiply the remainder by your marginal income tax rate. That is what you recover if the company fails. A 45% payer’s true worst case is 27.5p per pound; at 40% it is 30p; at 20%, 40p. Worked examples live in the loss relief guide.
Can I carry back SEIS relief to last year?
Yes. Any part of a subscription can be treated as if it were made in the previous tax year and claimed against that year’s bill, at the same 50%. It pays when last year’s liability was larger. The election and its deadlines are in the carry back guide.
Do you pay capital gains tax on SEIS shares?
Not if the shares qualify and you hold them at least three years: disposal relief makes the growth CGT-free, which is what the calculator’s exit comparison shows. Sell earlier, or lose SEIS status, and the exemption goes with it. The doors out are mapped in the exit guide.
What if I do not pay enough income tax to use the relief?
The relief can only reduce your bill to zero; nothing is refunded beyond what you actually owe. If this year’s liability is too small, carry back to last year often rescues the difference. The liability question is covered in the 50% explained.
How do I claim the relief this SEIS calculator shows?
Wait for the SEIS3 certificate from the company, then claim through Self Assessment or, for the current year, a PAYE coding adjustment. No SEIS3, no claim. The step-by-step route, including carry back boxes, is in how to claim SEIS tax relief.
Prefer the reading to the arithmetic?
Start with the plain-English guide to the whole scheme.
What is SEIS?