THE NUMBERS, EXPLAINED
How to use this calculator.
Two marginal tiers, not an all-units volume discount. Usage quantities and tier thresholds share the same billing unit.
Start with your inputs
Enter metered usage units, included allowance units, first overage tier width (units), first overage rate (currency/unit), remaining overage rate (currency/unit), base subscription fee (currency). Keep amounts in the units shown on each field. The example is a starting point, not a recommended value.
| Input | Example value |
|---|---|
| Metered usage units | 250 |
| Included allowance units | 100 |
| First overage tier width (units) | 100 |
| First overage rate (currency/unit) | 0.2 |
| Remaining overage rate (currency/unit) | 0.1 |
| Base subscription fee (currency) | 30 |
A worked example
With the example inputs above, first-tier billable units is 100. Change the inputs to explore your own scenario.
| Result | Example answer |
|---|---|
| First-tier billable units | 100 |
| Second-tier billable units | 50 |
| Usage invoice total (currency) | 55 |
How this is calculated
First-tier billable units
Apply the first marginal rate to usage immediately above allowance.
Second-tier billable units
Count usage beyond the allowance plus first tier.
Usage invoice total (currency)
Add base fee and the two marginal usage charges.
Symbols and units
- a
- Metered usage units
- b
- Included allowance units
- c
- First overage tier width (units)
- d
- First overage rate (currency/unit)
- e
- Remaining overage rate (currency/unit)
- f
- Base subscription fee (currency)
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
Two marginal tiers, not an all-units volume discount. Usage quantities and tier thresholds share the same billing unit.
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?
First-tier billable units; Second-tier billable units; Usage invoice total (currency). 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: Two marginal tiers, not an all-units volume discount. Usage quantities and tier thresholds share the same billing unit.
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
OpenStax: Describe and Identify Cost Drivers ↗
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 →