Will the pot actually last? Run 10,000 markets
The projection above assumes your return arrives smoothly every year. Real markets do not do that, and the order the good and bad years come in matters enormously once you start withdrawing. This simulation draws 10,000 random return sequences around your average and reports how many of them fund your income to the age you set.
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A success rate well under half is usually not a modelling error: it is sequence-of-returns risk. Withdrawing a fixed income while the pot is falling sells more units at low prices, and the pot never fully recovers when markets do. The same average return with the bad years at the end is comfortably survivable. Lowering the income you draw moves the number far more than raising the assumed return does.
What next?
A pension projection is a starting point. These are the checks that make it real.
External links are marked and open in a new tab. This is not financial advice — for a personal recommendation, use a regulated adviser.
What your result means
The projected pot is the nominal balance at your retirement age if returns average what you entered. In today’s money strips out inflation, which is the number worth planning around — it tells you what that pot would actually buy. The indicative income applies the widely-cited 4% withdrawal guideline as a rough sense of annual spending, not a guarantee.
Why this one is different
Rather than returning one figure, this runs 10,000 market paths in a background worker and reports the 10th, 50th and 90th percentile outcomes alongside a success rate. You set the return and inflation assumptions yourself instead of accepting hardcoded ones.
The first decade of contributions does most of the work
Money paid in at thirty has thirty-five years to compound; money paid in at sixty has five. In a typical projection the earliest fifth of your contributions can account for close to half the final pot, purely because it was invested longest.
Once the pot exists, the harder question is how long an income drawn from it will last. The SWP calculator answers that, and the SIP to SWP planner runs both phases in one pass so you can see the handover. If you are starting late, the lever that still works is the contribution rate rather than the return assumption. Raising monthly payments is under your control; chasing higher returns mostly raises the risk of a shortfall.
How it works
The projection compounds your existing pot forward monthly, then adds the future value of a regular monthly contribution stream at the same rate. Inflation is applied separately at the end to restate the result in today’s purchasing power.
How to use this calculator
- Choose your currency.
- Enter your current age and target retirement age.
- Add your current savings and monthly contribution.
- Set an expected return — long-run diversified portfolios have historically landed around 4–6% after charges.
- Read the pot in today’s money and treat it as a planning range, not a forecast.
Formula
P = current savings, C = monthly contribution, r = monthly return, n = months to retirement. Real value = FV ÷ (1 + inflation)^years.
Example calculation
Age 35, retiring at 67, with £25,000 saved and £400 a month at 5%:
You contribute ≈ £178,600
Growth ≈ £322,700
In today’s money (2.5% inflation) ≈ £227,500
Frequently asked questions
Why does the simulation give a much lower chance than the projection above?＋
Because the projection above compounds a single average return, while the simulation draws a different random sequence of returns for each of 10,000 runs. Averages hide the order of returns, and order is what decides whether a pot survives withdrawals. A plan that looks comfortable on an average return can still fail in half of realistic markets.
What return should I assume?＋
Be conservative. Long-run global equity returns have averaged mid-to-high single digits before charges, but a portfolio moving toward bonds near retirement returns less. Many planners model 4–5% after charges and test a pessimistic case too.
Does this include employer contributions?＋
Only if you add them. Combine your own payment and your employer’s into the monthly contribution figure — employer matching is usually the highest-return money in any pension.
What is the 4% rule?＋
A rule of thumb from US research suggesting a portfolio can sustain withdrawals of about 4% of its starting value, adjusted for inflation, for roughly thirty years. It is a starting point for discussion, not a safe-withdrawal guarantee.
What does the 4% rule actually claim?＋
That withdrawing four per cent of your starting pot in the first year, then adjusting that amount for inflation each year, historically had a high chance of lasting thirty years. It came from analysis of a specific market and period, assumes a particular asset mix, and is a rule of thumb rather than a guarantee.
Why does a bad year early in retirement matter more than a bad one later?＋
Because you are withdrawing from a portfolio that has just fallen, so you sell more units to fund the same income and there is less left to recover. The same poor year at the end does far less damage. This asymmetry is called sequence risk and it is the main danger a single average return figure hides.
Should I include the State Pension in my planning?＋
Include it, but separately from your own savings, since it starts at a set age and rises by its own rules. Knowing your forecast entitlement and its start date changes how much your own pot needs to cover — and often reveals a gap in the years before it begins.
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Assumptions & limitations
Every figure here comes from a simplified model. Keep these limits in mind when reading your result:
- The headline projection assumes a constant average return; real markets deliver that return unevenly. The simulation above is the check on that.
- The simulation draws returns from a normal distribution around your average. Real returns have fatter tails and some mean reversion, so it neither captures crashes fully nor the recoveries that follow them.
- Withdrawals in the simulation are a fixed real amount taken every year regardless of the pot. Real retirees cut spending in bad years, which raises survival rates materially.
- Charges, taxes and the state pension are excluded from both the projection and the simulation.
- Ignores tax relief, annual and lifetime allowances, charges and state pension entitlement.
- Contributions are assumed level in nominal terms — they are not increased with inflation or salary.
- The 4% income figure is illustrative only and is not a recommendation.