£100,000 is the threshold where tax efficiency genuinely dominates the investment decision — and where one structuring mistake can cost tens of thousands of pounds. Before you move a penny, three questions determine your entire strategy.

First, and most urgent: do you earn between £100,000 and £125,140? If so, your effective marginal income tax rate is 60%. Every £2 of income above £100k removes £1 of your £12,570 personal allowance, taxed at 40% — the combined effect is 60p tax cost per £1 of marginal income. Every £1 you contribute to a SIPP at this income level saves 60p in tax. A £50,000 SIPP contribution at this bracket costs an effective £20,000 net after relief. Second: have you used your £20,000 ISA allowance? Use-it-or-lose-it by 5 April. Third: have you explored SIPP carry-forward? You can carry unused pension allowance from the 3 prior tax years — if you contributed little or nothing in 2022–25, you could potentially contribute up to £180,000 extra, subject to having sufficient UK earnings.

At £100,000, this calculator provides the framework. An FCA-authorised fee-only financial planner (typically £1,000–£3,000 for a full plan) will almost certainly save their fee multiple times over in tax optimisation — particularly around the personal allowance trap, SIPP carry-forward, and Inheritance Tax planning if applicable.