Examples
Examples
Try the starting example
- Measured usable bag capacity (L)
- 10
- Measured fill per week (L)
- 2
- Current fill in fitted bag (L)
- 0
- Weeks to budget
- 10
- Unused spare bags
- 0
- Bags per retail pack
- 4
- Pack price ($)
- 12
- Budget start date
- 2026-10-20
- Replacements during horizon
- 2
- Next replacement date
- 2026-11-24
- Retail packs to buy
- 1
- Purchase cost ($)
- $12.00
- Unused spare bags after horizon
- 2
Try another scenario
- Measured usable bag capacity (L)
- 10
- Measured fill per week (L)
- 2
- Current fill in fitted bag (L)
- 0
- Weeks to budget
- 10
- Unused spare bags
- 2
- Bags per retail pack
- 4
- Pack price ($)
- 12
- Budget start date
- 2026-10-20
- Replacements during horizon
- 2
- Next replacement date
- 2026-11-24
- Retail packs to buy
- 0
- Purchase cost ($)
- $0.00
- Unused spare bags after horizon
- 0
Calculation method
Calculation method
Replacements during horizon
Round down (current fill + weeks × weekly fill) / usable capacity. An exactly full bag is replaced at that point.
Next replacement date
Start plus the ceiling of days to fill the current bag; report no replacement when weekly fill is zero.
Retail packs to buy
Round up max(0, replacements − existing spares) / pack size.
Purchase cost ($)
Packs × pack price.
Unused spare bags after horizon
Existing spares + purchased bags − replacement count.
Symbols and units
- a
- Measured usable bag capacity (L)
- b
- Measured fill per week (L)
- c
- Current fill in fitted bag (L)
- d
- Weeks to budget
- e
- Unused spare bags
- f
- Bags per retail pack
- g
- Pack price ($)
- h
- Budget start date
Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.
Assumptions & limits
Assumptions & limits
- Budget from measured fill volume under constant use. The horizon is a supplied number of weeks, not an assumed calendar year. Capacity and replacement practice must come from your product records.
Are these inputs private?
These calculations run in your browser. A shared link contains the values you choose to share. Only questions submitted to the separate AI finder are sent to OpenAI.
Further reading
OpenStax: arithmetic and geometry ↗
Background reading; this does not imply endorsement or independent review of SumFizz.