Updated for 2025/26 tax year
The Complete Guide to Share Incentive Plan Calculators
How to calculate your SIP tax savings, understand HMRC thresholds, and make the most of one of the UK’s most generous employee share schemes.
Section 01
What is a Share Incentive Plan?
A Share Incentive Plan — or SIP — is a government-approved employee share scheme that lets you buy or receive shares in your employer completely free of Income Tax and National Insurance, provided you hold them for long enough. It sits alongside EMI options and SAYE schemes as one of HMRC’s four approved arrangements, but it’s arguably the most straightforward to understand.
The core idea is simple: your employer can give you shares, and you can buy shares directly from your pre-tax salary. Because the money never officially enters your take-home pay before going into the scheme, you never owe tax on it. That alone can shave hundreds — sometimes thousands — off your annual tax bill.
There are four distinct types of shares that can sit inside a SIP — free shares, partnership shares, matching shares, and dividend shares. Not every employer offers all four, but understanding each one helps you squeeze the most value from whatever your company does provide.
Who can use a SIP?
Any UK employer can set up a SIP for its employees, though they’re not obligated to. If your employer does offer one, all eligible employees must be invited to participate on the same terms — the scheme cannot cherry-pick individuals.
Section 02
How a SIP calculator works
A Share Incentive Plan calculator takes the inputs specific to your situation and works out your real-terms financial benefit — including exactly how much Income Tax and National Insurance you avoid paying. Unlike generic tax calculators, a good SIP tool accounts for your marginal tax rate, the type of shares you hold, how long you’ve held them, and any matching shares your employer contributes.
At its heart, the maths behind a SIP calculator is not complex. The saving comes from the fact that partnership shares are purchased from gross pay, not net pay. So if you earn enough to be a basic-rate taxpayer and you invest £1,000 in partnership shares, you only “feel” a cost of roughly £680 — because the £320 that would have gone to Income Tax and NI never left your salary in the first place.
What a good calculator should ask you
To produce an accurate result, a SIP calculator needs at least the following information:
Your annual gross salary
This determines your marginal tax rate, which drives most of the calculation. A higher earner in the 40% bracket saves proportionally more than a basic-rate taxpayer.
How much you invest in partnership shares
Up to £1,800 per year (or 10% of salary if lower). This is the amount deducted from your pre-tax pay.
Your employer’s matching ratio
Many employers offer one or two matching shares for every partnership share you buy. This free equity is a huge part of the SIP’s appeal.
Any free shares your employer awards
Up to £3,600 worth of shares gifted to you annually, with no cost to you and no Income Tax if held for five years.
How long you plan to hold the shares
The holding period determines whether you owe Income Tax on removal. The calculator adjusts your net benefit accordingly.
Section 04
Step-by-step calculation example
Let’s walk through a realistic worked example. Meet Sarah — she earns £45,000 per year as a marketing manager at a listed company. Her employer offers a SIP with a 1:1 matching ratio, and also awards £1,500 in free shares each year.
Sarah decides to invest the maximum into partnership shares. Here’s exactly what that looks like for the 2025/26 tax year:
That £4,254 combines her direct tax saving of £954 with £3,300 worth of shares she received at no cost (matching plus free shares). Her actual out-of-pocket cost for the partnership shares, after tax and NI relief, was just £1,296 rather than £1,800.
Higher-rate taxpayers save even more
If Sarah earned £60,000 instead, her marginal tax rate would jump to 40%. Her Income Tax saving on partnership shares alone would double to £720 — and if she withdraws after five years, the free shares would also escape the 40% rate entirely.
Section 05
HMRC 2025/26 thresholds
HMRC sets the annual limits for SIPs by legislation, and they do not change every year in the way that ISA allowances do. For the 2025/26 tax year, the thresholds remain as follows:
| Share type | 2025/26 limit | Notes |
|---|---|---|
| Free shares | £3,600 per employee | Employer decides the allocation method (equal, performance-based, or by salary). Must be within HMRC rules. |
| Partnership shares | £1,800 or 10% of salary (whichever is lower) | Deducted from gross pay before tax. Accumulation periods of up to 12 months are allowed. |
| Matching shares | Up to 2 for every partnership share | Employer chooses the matching ratio. Must apply equally to all participants. |
| Dividend shares | £1,500 of dividends reinvested | Dividends on all SIP shares can be reinvested into further shares within the plan. |
Income Tax and NI rates used in SIP calculations
| Taxpayer type | Taxable income (2025/26) | Income Tax rate | Employee NI | Combined rate |
|---|---|---|---|---|
| Basic rate | £12,571 – £50,270 | 20% | 8% | 28% |
| Higher rate | £50,271 – £125,140 | 40% | 2% | 42% |
| Additional rate | Over £125,140 | 45% | 2% | 47% |
Watch the £100,000 trap
If your gross salary sits between £100,000 and £125,140, you lose £1 of Personal Allowance for every £2 earned over £100,000. This creates an effective marginal rate of 60%. Contributing to partnership shares reduces your adjusted net income, which can restore some or all of your Personal Allowance — making the effective SIP saving even greater for this group.
Ready to work out your own saving?
Use our free calculator to enter your salary, employer matching ratio, and free share award — and see exactly what your SIP is worth this tax year.
Open the Share Incentive Plan CalculatorSection 06
5 common SIP questions answered
Can I sell my SIP shares before five years without a tax penalty?
Yes, but there will be a tax cost. Withdrawing partnership shares or free shares within three years means you pay Income Tax and National Insurance on their market value at the time of withdrawal — essentially reversing the upfront tax saving. Between three and five years, you pay tax on whichever is lower: the original acquisition cost or the current market value. Only after five years do you walk away with no Income Tax or NI charge at all. That said, Capital Gains Tax may still apply on any price growth.
What happens to my SIP shares if I leave my job?
Leaving your employer triggers what’s called a “leaving event.” Your shares must be removed from the plan, and whether you face a tax charge depends on how long you’ve held them. There are some exceptions — if you leave due to redundancy, retirement, disability, or death, HMRC treats it as if you’d held the shares for the full five years, meaning no Income Tax or NI charge regardless of the actual holding period. It’s worth checking your specific plan rules, as some employers also have provisions around shares being sold on exit.
Do SIP shares count towards my ISA allowance?
SIP shares and ISAs are entirely separate. Your SIP participation does not reduce your annual ISA allowance (£20,000 for 2025/26). However, you can transfer shares from a SIP into a stocks and shares ISA within 90 days of them leaving the plan, which shelters any future growth and income from tax. This is one of the most underused advantages of a SIP — it effectively gives you a backdoor route to sheltering shares in an ISA without using your annual ISA cash allowance.
How does a SIP accumulation period affect the calculation?
Some employers run accumulation periods — typically 6 or 12 months — where your salary deductions are held in a ring-fenced account before being used to buy partnership shares in one batch. During accumulation, the money sits as cash rather than shares. If the share price rises during this time, you miss out on gains; if it falls, you buy in at a lower price. Your accumulation period also affects when the five-year clock starts — it begins from the date the shares are actually purchased, not when the deductions started. A SIP calculator should account for your specific accumulation period when estimating your total benefit.
Is a SIP better than a pension for tax savings?
They serve different purposes, so the comparison isn’t quite apples to apples. Both give you upfront relief on Income Tax and NI contributions. However, pensions are locked until age 57 (rising to 58 in 2028), while SIP shares are accessible — with some tax consequence — from day one. Pensions also benefit from employer contributions and potentially greater long-term compounding. On the other hand, a SIP lets you invest in your employer’s specific shares and often comes with free matching shares that pensions typically don’t offer. For most people, the right answer is to maximise both where possible, starting with any employer-matched contributions in either vehicle.