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Share Incentive Plan (SIP) Calculator

Calculate the upfront Income Tax and National Insurance saving from buying UK Share Incentive Plan (SIP) Partnership Shares, plus your Matching Shares and total value if held the full 5-year tax-free period.

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The upfront saving reflects the Income Tax and NI relief on your Partnership Share purchase. The 5-year total assumes you hold all shares for the full qualifying period, at which point no further Income Tax or NI is due on withdrawal.

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How UK Share Incentive Plan Tax Relief Works

A Share Incentive Plan (SIP) lets UK employees buy company shares directly from salary before Income Tax and National Insurance are deducted — the tax relief happens upfront, at the point of purchase, not just on eventual gains.

How to Calculate Your SIP Tax Saving

Upfront Saving = Partnership Share Amount × Combined Tax Rate, where the combined rate depends on your Income Tax band: 28% for basic rate (20% Income Tax + 8% NI), 42% for higher rate (40% + 2% NI, since NI drops above the upper earnings limit), or 47% for additional rate (45% + 2% NI).

Share Incentive Plan Calculator Formula

  1. Upfront Saving = Partnership Share Amount × Combined Rate %
  2. Effective Cost = Partnership Share Amount − Upfront Saving
  3. Matching Shares Value = Partnership Share Amount × Employer Matching Ratio
  4. Total Value if Held 5+ Years = Partnership Shares + Matching Shares (tax-free at this point)

Why Do Higher-Rate Taxpayers Save 42%, Not 48%?

Because National Insurance drops from 8% to just 2% above the £50,270 upper earnings limit — and higher-rate taxpayers, by definition, earn above that threshold. So their marginal saving combines the 40% Income Tax rate with only the 2% NI rate, not the 8% rate that applies to basic-rate earners.

SIP Tax Saving Examples

Higher-rate taxpayer, full annual limit: £1,800 in Partnership Shares at the 42% combined rate saves £756 upfront, for an effective cost of £1,044. With 1:1 Matching Shares, total value if held 5+ years reaches £3,600.

Common SIP Planning Mistakes

Assuming the tax saving is the same across all tax bands — it isn't, due to the NI threshold effect described above. Not planning for the 5-year holding period — leaving the plan early triggers Income Tax and NI on withdrawal, which this calculator's headline saving doesn't reflect. Forgetting that Partnership Shares still carry investment risk — the tax relief reduces your effective cost, but the shares themselves can still lose value.

How to Use This Calculator

Enter how much you want to invest in Partnership Shares (up to £1,800/year), select your Income Tax band, and enter your employer's Matching Share ratio.

Formula & Methodology

Partnership Shares are bought from pre-tax, pre-NI salary. Upfront Saving = Partnership Share Amount × Combined Rate, where the combined rate depends on your tax band: 28% for basic rate (20% Income Tax + 8% NI), 42% for higher rate (40% + 2% NI — NI drops to 2% above the £50,270 upper earnings limit), or 47% for additional rate (45% + 2% NI). Matching Shares Value = Partnership Share Amount × Matching Ratio.

Example: £1,800 Partnership Shares, higher-rate taxpayer, 1:1 matching

Upfront saving = £1,800 × 42% = £756. Effective cost = £1,800 − £756 = £1,044. Matching shares value = £1,800 × 1 = £1,800. Total value if held 5+ years = £1,800 + £1,800 = £3,600, for an effective cost of £1,044 — tax-free if held the full period.

This covers Partnership Shares and Matching Shares only — Free Shares (up to £3,600/year, given at no cost) and Dividend Shares are separate SIP components not calculated here. This calculator assumes your Partnership Share deduction falls entirely within a single tax band and does not model earnings that straddle two bands. It shows the 5-year holding outcome only (£0 tax) — it does not calculate the partial tax due if shares are withdrawn between 3-5 years (tax on the lower of award value vs. withdrawal value) or within 3 years (full tax on withdrawal value), since these depend on share price movements and 'good leaver' status that can't be generalized. It also does not model the National Insurance secondary/marginal-band edge case for employees whose partnership share deduction would straddle the £50,270 threshold itself.

This is a general planning estimate based on 2026/27 UK tax rates, not personalized tax advice. Share values can go down as well as up, and your specific circumstances (total income, other deductions, Scottish tax bands, employer plan rules) may change your actual position. Confirm your specific numbers with your employer's SIP administrator, HMRC, or a qualified financial adviser.

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Frequently Asked Questions

How much can I invest in Partnership Shares?
Up to £1,800 per tax year, or 10% of your salary, whichever is lower — this is the HMRC limit for the 2026/27 tax year.
Why is my National Insurance saving only 2%, not 8%, as a higher-rate taxpayer?
Because higher-rate taxpayers earn above the £50,270 upper earnings limit, their marginal National Insurance rate on additional income is 2%, not the 8% rate that applies within the basic-rate band. This is why a higher-rate taxpayer's combined saving is 42% (40% Income Tax + 2% NI), not 48%.
How many Matching Shares can I get?
Your employer can award up to 2 Matching Shares for every 1 Partnership Share you buy, at whatever ratio they choose to offer (commonly 1:1 or lower).
What happens if I withdraw my shares before 5 years?
If withdrawn within 3 years, Income Tax and NI are due on the shares' market value at withdrawal. Between 3-5 years, tax is due on the lower of the original value or the withdrawal-date value. This calculator shows the 5-year outcome (£0 tax) — see Limitations for why early-withdrawal amounts aren't calculated here.
Is this the same as Free Shares?
No — this calculator covers Partnership Shares (bought with your own pre-tax salary) and Matching Shares (given by your employer based on your Partnership Share purchase). Free Shares are a separate SIP component (up to £3,600/year, given at no cost) not covered by this calculator.
Are Partnership Shares risk-free?
No — Partnership Shares are real company shares, and their value can go down as well as up. The tax/NI saving reduces your effective cost, but you still bear the investment risk on the shares themselves.

Last updated 7/15/2026