THE NUMBERS, EXPLAINED
How to use this calculator.
Multiply essential monthly expenses by the coverage period you choose. This tool does not prescribe a reserve size.
Start with your inputs
Enter monthly essentials (£), target months, existing reserve (£). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Monthly essentials (£) | 1500 |
| Target months | 6 |
| Existing reserve (£) | 3000 |
A worked example
With the example inputs above, target reserve (£) is 9,000. Change the inputs to explore your own scenario.
Putting the example numbers into the formula
Target reserve (£)
(1500) × (6) = 9,000
Shortfall (£)
max(0,(1500) × (6)-(3000)) = 6,000
| Result | Example answer |
|---|---|
| Target reserve (£) | 9,000 |
| Shortfall (£) | 6,000 |
How this is calculated
Target reserve (£)
a × b
Shortfall (£)
max(0,a × b-c)
Symbols and units
- a
- Monthly essentials (£)
- b
- Target months
- c
- Existing reserve (£)
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
max(x, y, …) selects the largest value.
Assumptions and limits
Multiply essential monthly expenses by the coverage period you choose. This tool does not prescribe a reserve size.
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?
Target reserve (£); Shortfall (£). 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: Multiply essential monthly expenses by the coverage period you choose. This tool does not prescribe a reserve size.
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.
Read the quality report →