THE NUMBERS, EXPLAINED
How to use this calculator.
An ordinary annuity pays at each period end. The zero-rate limit is payment × number of payments.
Start with your inputs
Enter payment per period (£), rate per period (%), number of payments. Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Payment per period (£) | 100 |
| Rate per period (%) | 0 |
| Number of payments | 12 |
A worked example
With the example inputs above, future value (£) is 1,200. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| Future value (£) | 1,200 |
| Present value (£) | 1,200 |
How this is calculated
Future value (£)
Let q = b/100. Future value = a × ((1+q)^c−1)/q; if q = 0, use a × c.
Present value (£)
Let q = b/100. Present value = a × (1−(1+q)^(−c))/q; if q = 0, use a × c.
Symbols and units
- a
- Payment per period (£)
- b
- Rate per period (%)
- c
- Number of payments
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions and limits
An ordinary annuity pays at each period end. The zero-rate limit is payment × number of payments.
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?
Future value (£); Present value (£). 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: An ordinary annuity pays at each period end. The zero-rate limit is payment × number of payments.
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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