What your result means
This mode runs your plan end to end. The pot at start of withdrawals is the exact corpus your SIP produced — not a round number you guessed — and it becomes the opening balance for the income phase. Getting that handover right is the whole point.
The headline is how long the income lasts once it starts. Read it alongside the corpus figure: those two numbers together tell you whether the years you spent contributing actually bought the retirement you had in mind, or whether you need a larger SIP, a longer accumulation, or a smaller income.
If the answer disappoints, the most powerful lever is almost always the length of the investing phase rather than the size of the contribution. Five more years of compounding at the end of the accumulation period does more than a substantial increase in the monthly amount, because that money compounds on the largest balance you will ever have.
The day you stop paying in is the day the risk changes completely
For thirty years, a falling market is an opportunity — your monthly contribution buys more units. On the day you switch to withdrawing, that same falling market becomes the biggest threat to the plan, because now you are selling units instead of buying them.
Running both phases in one calculation is the only way to see that pivot. Switch on the stress test and put five bad years right at the handover: it is consistently the most sobering thing this calculator does, and it is exactly the scenario a two-calculator plan hides.
How it works
The accumulation phase runs exactly like a standard SIP: monthly contributions, monthly compounding, charges deducted from the balance, optional annual step-ups. Its closing balance carries straight through.
The withdrawal phase then begins with that balance and your original total contributions as the cost basis, so the tax calculation knows how much of every later withdrawal is genuinely gain rather than your own money coming back.
The year-by-year table runs continuously across both phases, with the "paid in" column switching to withdrawals at the handover — so you can see the peak balance and the point the curve turns over.
How to use this calculator
- Enter your monthly investment and how many years you will invest for.
- Enter the monthly income you want once the withdrawals start.
- Set the expected return — you can use one rate for the whole plan, or run it twice with a lower rate for the withdrawal years.
- Add inflation, charges and tax in Advanced options.
- Turn on the stress test to put five bad years at the handover, which is the worst possible timing.
Formula
C = the corpus at handover, which becomes B0 for the withdrawal phase. P = monthly contribution, W = monthly withdrawal, i = net monthly return, n = months of investing.
Worked example
£500 a month for 20 years at 11%, then withdrawing £4,500 a month rising 3% a year:
Pot at handover £407,804
Income then lasts 11 years 4 months
Total withdrawn £714,147
With five bad years at handover:
Income lasts 6 years 8 months
Twenty years of disciplined investing buys about eleven years of a £4,500 income — and barely half that if the market turns at the wrong moment. That is not an argument against the plan, it is an argument for knowing the number before you retire on it. Dropping the income to £3,000 makes the same pot last indefinitely.
Frequently asked questions
Can I use different returns for the two phases?＋
Not in a single run, because the tool uses one expected return throughout. Most people shift to a lower-risk mix at retirement, so a fair approach is to run the plan twice — once at your growth rate to find the corpus, then in SWP mode with that corpus and a lower rate for the income phase.
When should I switch from investing to withdrawing?＋
The calculator answers the version of that question you can act on: for a given income, how many years of contributions do you need. Change the investing period and watch how long the income lasts — you will usually find a point where a couple of extra years transforms the outcome.
Why does the income last so much less time than I invested?＋
Because you are withdrawing far more each month than you ever paid in. Contributing £500 and drawing £4,500 is a nine-fold difference; twenty years of the first does not fund twenty years of the second unless the pot is very large or the return very high.
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Assumptions & limitations
A two-phase plan inherits the limits of both halves:
- Returns are assumed constant every year. Real markets are not — they deliver the average through a sequence of good and bad years, and the order those arrive in changes the outcome.
- Growth is compounded monthly from the annual rate you set, so 10% a year becomes 0.797% a month rather than a flat 0.833%.
- Fund charges are deducted monthly from the balance. Platform fees, trading costs and bid-offer spreads are not modelled separately — fold them into the charge figure if you want the full picture.
- Inflation is applied at a single constant rate to produce the "today's money" figures. Your personal inflation rate depends on what you actually buy.
- Nothing here is financial advice, and no projection is a promise. Use it to compare scenarios against each other, not to predict a number.
- A single expected return is used for both the investing and the withdrawing years, though most people de-risk at the handover.
- The switch from contributing to withdrawing happens instantly, with no gap and no partial retirement.