THE NUMBERS, EXPLAINED
How to use this calculator.
Withdraw at each year start, then apply the assumed annual return. Constant-return scenarios omit market volatility and are not retirement advice.
Start with your inputs
Enter starting fund (£), initial annual withdrawal (£), annual return (%), annual withdrawal inflation (%), horizon years. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Starting fund (£) | 100000 |
| Initial annual withdrawal (£) | 10000 |
| Annual return (%) | 0 |
| Annual withdrawal inflation (%) | 0 |
| Horizon years | 20 |
A worked example
With the example inputs above, years funded is 10. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Years funded | 10 |
How this is calculated
Years funded
fundedYears(a,b,c,d,e)
Symbols and units
- a
- Starting fund (£)
- b
- Initial annual withdrawal (£)
- c
- Annual return (%)
- d
- Annual withdrawal inflation (%)
- e
- Horizon years
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Calculation steps and notation
At each year’s start, check whether the balance covers the withdrawal. If it does, subtract the withdrawal, grow the remaining balance by (1 + annual return/100), and increase next year’s withdrawal by (1 + withdrawal growth/100). Count fully funded years, up to the chosen horizon.
Assumptions and limits
Withdraw at each year start, then apply the assumed annual return. Constant-return scenarios omit market volatility and are not retirement advice.
Calculations use the values you enter. Blank or invalid inputs show an error instead of silently substituting zero. Results are displayed to useful precision; calculations retain the underlying numeric precision.
Questions about this tool
What does the result tell me?
Years funded. The result applies to the method and inputs described above. Check the units and assumptions before using it in a decision.
Why might another calculator differ?
Differences in units, rounding, timing or model definitions can produce different answers. Compare the input definitions and the method, rather than only the final number. For this tool: Withdraw at each year start, then apply the assumed annual return. Constant-return scenarios omit market volatility and are not retirement advice.
Are my inputs stored or sent to AI?
Calculations on this page happen in your browser. The separate AI question finder sends its submitted conversation to OpenAI; these calculator fields are not sent. Favourites and recent tool names are stored locally. A shared link contains the inputs you choose to include.
Further reading
Investor.gov: financial planning tools ↗
Background reading; this does not imply endorsement or independent review of SumFizz.
Review status
Software example and browser checks are recorded in our quality report. No external expert review is claimed. Created with coding assistance; calculations run as ordinary browser code.
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