Share Incentive Plan Calculator

1. Enter your annual salary and the annual amount you want to contribute to partnership shares (up to £1,800/year, taken pre-tax from gross salary).
2. Set the employer matching ratio — most employers offer 1:1 or 2:1 (£1 matching per £1 you contribute, or £2 per £1). Maximum matching shares are capped at £3,600/year regardless of ratio.
3. Enter annual free shares your employer awards (separate from matching, up to £3,600/year).
4. Set expected growth and holding period. Growth = annual share price appreciation. Holding period = years shares stay in the SIP trust before sale.
5. Enter your marginal income tax rate (UK basic 20%, higher 40%, additional 45%). This determines your tax savings from buying shares pre-tax.

The UK Share Incentive Plan (SIP) is one of the most tax-efficient ways for UK employees to acquire shares in their employer. The math benefits compound across three tax savings.

Annual Contribution Value =
  Partnership Shares (your pre-tax money, up to £1,800)
+ Matching Shares (free, up to 2:1 your contribution, max £3,600)
+ Free Shares (employer-awarded, up to £3,600)

Tax Saving per year = Partnership × (Income Tax Rate + NI Rate)
Tax-Free Sale (5+ years held) = no IT, no NI, no CGT

Example: Higher-rate taxpayer (40%) contributing the £1,800 maximum, with 2:1 employer matching and £1,200/year free shares, held 5 years at 5% annual growth.

• Annual partnership: £1,800 (your money, saves £864 in tax+NI annually)
• Annual matching: £3,600 (free from employer)
• Annual free shares: £1,200
• Total annual contribution: £6,600 of shares
• 5-year portfolio value at 5% growth: ~£37,000
• Your cost: £9,000. Tax-free profit at sale: £28,000+

UK employees often have multiple share scheme options. SIP is one of three approved tax-advantaged plans, each with different trade-offs.

Three rules of thumb:

• SIP wins if your employer offers free or matching shares. Free money + tax-free sale is hard to beat. Always max out SIP first if matching/free shares are available.
• SAYE wins for risk-averse employees. You save into a regular savings account; only exercise the share option if the price has gone up. Worst case, you get your money back with a small bonus.
• Hold all SIP shares 5+ years. Selling early loses income tax + NI advantages, often wiping out years of tax savings. The 5-year rule is the single most important SIP optimization.

For UK employees with the maximum contributions available, SIP can effectively triple the after-tax value of the "share allocation" portion of compensation compared to receiving the equivalent cash salary.