Will your money last in retirement?
A free UK Monte Carlo retirement calculator. Run 5,000 simulated futures of your plan, with real UK tax baked in. Five inputs, instant answer, no signup.
Your pot over time — worst case to best case
The full WealthR app runs this on every £ you've tracked.
This is a foot-in-the-door version with 5 inputs. The real engine inside WealthR pulls your actual ISA balance, every SIPP and DB pension you have, partner pensions, BTL income, property equity, plus your full UK tax — Scottish rates, HICBC, Marriage Allowance, top-slicing relief. Free to start, two minutes to set up.
- Your real ISAs, SIPPs, DB and State Pension
- Partner pensions and joint household view
- Scottish rates, HICBC and Marriage Allowance
- Sequence-of-returns stress test
- Save and compare multiple scenarios (Pro)
- PDF report you can share with an IFA (Pro)
What does a Monte Carlo retirement calculator actually do?
Most retirement calculators take one fixed growth rate — say 5% — and tell you "you'll have £620,000 at 67." That number is a fantasy because markets don't deliver 5% every year. Some years they're up 25%, some they're down 30%. The order those returns arrive matters enormously, especially in retirement when you're drawing down. A crash in your first two years of retirement can drain a pot that the same average return would have left untouched if it had crashed ten years later.
A Monte Carlo simulation takes your plan and replays it five thousand times. Each replay uses a different random sequence of yearly returns drawn from how the market has actually behaved over the last century. Then it counts: in how many of those 5,000 replays did your money last to age 95? If the answer is 4,100, that's an 82% chance of success. It's the difference between "your pension statement says you'll have £620k" (one made-up future) and "across 5,000 plausible futures, the median is £620k, the worst case is £180k, the best case is £2.4M, and 82% of them leave you okay."
How to read the result
The big number is the percentage of simulated futures where your pot lasted to age 95. Most planners target 80%–95%. Below 65% is uncomfortable. Below 50% is a wake-up call. Above 95% probably means you're saving more than you need to — there's such a thing as over-saving.
The fan chart shows the spread of outcomes year by year. The bold green line is the median: half of futures landed above it, half below. The darker green band covers the middle 50% (the "likely" range). The lighter outer band shows the full 10th–90th percentile spread — what the worst-case 1-in-10 and best-case 1-in-10 futures look like. If the lower edge of the chart bottoms out before your target age, that's where your worst-case retirement runs out.
What this simulator captures — and what it doesn't
It captures: sequence-of-returns risk (the order of returns), volatility (year-to-year swings), UK income tax on drawdown (Personal Allowance, basic and higher rate), the 25% SIPP tax-free portion, and State Pension if you tick the box. Returns are sampled from a log-normal distribution with a 5% mean real return and 12% volatility — typical of a globally diversified equity portfolio over the last century. All figures are in today's pounds (real terms), so you don't have to mentally adjust for inflation.
It does not capture: Scottish rates, HICBC, Marriage Allowance, dividend allowances, partner pensions, multiple separate pots with different drawdown ages, BTL rental income, top-slicing relief, or the personal allowance taper above £100k. The full WealthR app handles all of those because it has your real data to work with.
This is a planning aid, not regulated financial advice. See the full methodology for the underlying maths and assumptions.