UK tax year 2026/27 · For Ltd Co directors & the self-employed
Most tax calculators are mathematically wrong.
Ours aren't.
Every "how much will I have at retirement" tool gives you a single number. The truth is a distribution. BracketMath uses proper Monte Carlo simulation, joint tax optimisation, and sequence-of-returns risk — the same methods used by actual quants — to tell you what's really optimal for your situation.
What everyone else gets wrong
Point estimates
Other sites tell you "you'll have £450k at retirement." That's the mean. Returns are random. Your actual outcome is anywhere from £180k to £900k. We show you the full distribution.
Greedy optimisation
Most calculators optimise salary or dividends or pension separately. The UK tax code has interaction effects. We optimise jointly using Lagrangian methods.
No volatility
They ignore sequence-of-returns risk — a crash in year 1 of retirement is catastrophically different from year 20. We model 10,000 paths through your retirement.
Three calculators that will save you thousands
1. Salary–Dividend Split Optimiser
If you're a Ltd Co director, the wrong salary–dividend split costs you £500–£3,000 a year. Our optimiser searches the joint space of (salary, dividend, pension contribution) and finds the single point that minimises your effective tax rate across both corporation tax and personal tax. It also tells you the gradient: how much each £1 of additional salary costs you in total tax.
2. SIPP Contribution Optimiser
How much should you actually contribute to your SIPP this tax year? We compute the answer using Monte Carlo simulation over 10,000 future paths, modelling realistic asset returns with autocorrelation and crash probability. Result: an optimal contribution plus a fan chart showing the 5th, 50th, and 95th percentile of your retirement pot.
3. Take-Home Calculator (Inside vs Outside IR35)
The real net of any contract, factoring in VAT scheme, dividend tax, NI, corporation tax, and employer NI rebate. Side-by-side inside vs outside IR35 comparison with the break-even day rate explicitly shown.
Methodology, in one paragraph
Every calculation on this site uses the published HMRC rates for the 2026/27 tax year. Returns are modelled using block-bootstrap resampling of historical UK equity and gilt returns from 1900–2024, preserving the autocorrelation structure that destroys naive Monte Carlo. Optimisations use SciPy-style bounded numerical methods on the joint tax function, not greedy single-variable searches. Calculations run entirely in your browser — we don't store anything, ever. Full methodology: read the technical write-up →