The £100,000 trap is brutal for people with equity pay, because RSU vests are lumpy and easy to forget when you think about your income.
Why vests are dangerous near £100k
Your salary might sit comfortably below £100,000, but RSU vests are added to it as taxable income. A £90,000 salary plus £15,000 of vests is £105,000 of taxable employment income before relevant adjustments. Check pension contributions, other taxable income and Gift Aid before treating that as adjusted net income. You lose personal allowance at £1 for every £2 above £100,000, and if you have young children you can lose Tax-Free Childcare and eligibility for England's working-parent funded hours. Universal 15 hours for three- and four-year-olds are separate and remain available regardless of income.
A common option: pension contribution
For many people in this position, bringing your adjusted net income back to £100,000 with a pension contribution is worth exploring. Salary sacrifice is usually the most efficient route because it also saves National Insurance. A relief-at-source pension or a Gift Aid donation reduces ANI by the same gross amount. Whether any of these makes sense depends on your circumstances -- the calculator shows what the numbers look like.
The exact contribution you need is the amount your ANI exceeds £100,000. The calculator shows it for your numbers, along with the personal allowance you reclaim.