Understanding Your Results
Capacity remaining is rated litres minus litres used, with a minimum of zero. The forecast chooses the earlier of capacity exhaustion and the manufacturer calendar limit, measured from the current count date.
The quantity beside the item name is the stock value used for LOW STOCK: quantity at or below your minimum triggers that status. Additional days, cycles, sets or dates describe the entered assumptions; they are not a live measurement. Recount after use, receipt or relocation. A different device reads the printed snapshot and does not automatically receive later inventory changes.
The forecast assumes the entered five-litre daily use continues.
Practical Examples
These are illustrative household inputs, not product specifications or recommended use rates. Enter each record below, select Calculate & Save, and compare the displayed calculation.
Let capacity determine the earlier filter review
The measured capacity remainder runs out before the calendar limit.
Enter the installation date and the date represented by the usage count.
Inputs: Rated capacity (litres): 600; Litres already used: 500; Litres used per day: 5; Installation date: 2026-01-01; Date of current usage count: 2026-02-01; Manufacturer maximum calendar life (days): 180.
Result: Capacity remaining = max(0, 600 − 500) = 100 litres; 100 ÷ 5 = 20 days. Calendar limit 2026-06-30; earlier estimated review 2026-02-21 (20 days from count date). Saved quantity: 100 litres.
Twenty capacity days determine a February 21 review.
The forecast assumes the entered five-litre daily use continues.
Read the full worked exampleLet the calendar limit determine the earlier review
Much capacity remains, but the entered time limit is close.
Compare both constraints rather than reading capacity days alone.
Inputs: Rated capacity (litres): 600; Litres already used: 100; Litres used per day: 5; Installation date: 2026-01-01; Date of current usage count: 2026-02-01; Manufacturer maximum calendar life (days): 40.
Result: Capacity remaining = max(0, 600 − 100) = 500 litres; 500 ÷ 5 = 100 days. Calendar limit 2026-02-10; earlier estimated review 2026-02-10 (9 days from count date). Saved quantity: 500 litres.
The nine-day calendar remainder gives a February 10 review.
The forty-day limit is a user-entered example, not a universal rating.
Read the full worked exampleRecognize a cartridge already past its entered time limit
The usage count is taken after the recorded calendar life ends.
Read the zero-day review result alongside the past calendar limit.
Inputs: Rated capacity (litres): 600; Litres already used: 100; Litres used per day: 5; Installation date: 2026-01-01; Date of current usage count: 2026-03-01; Manufacturer maximum calendar life (days): 40.
Result: Capacity remaining = max(0, 600 − 100) = 500 litres; 500 ÷ 5 = 100 days. Calendar limit 2026-02-10; earlier estimated review 2026-03-01 (0 days from count date). Saved quantity: 500 litres.
The review is due at the count date despite remaining capacity.
Follow product instructions rather than treating this estimate as performance certification.
Read the full worked exampleCommon Mistakes to Avoid
Do not enter a zero daily rate to hide exhausted capacity. Capacity provides zero additional days. The tool does not measure actual filtration quality.
Negative remaining litres would not represent usable capacity. Remaining capacity is clamped to zero. The rating itself must be copied from the correct product.
Changing the used-volume count would alter the wrong assumption. The capacity estimates are fifty and ten days respectively. Daily use must come from observation rather than this calculator.
How do I compare lower and higher observed water use?
Treat the two rates as alternatives rather than separate cartridges. The capacity estimates are fifty and ten days respectively.
Daily use must come from observation rather than this calculator.
How do I update a measured usage count one month after installation?
Update both used volume and its count date. The revised capacity remainder is 690 litres.
A count is manually entered, not read from a sensor.
How do I calculate a water-filter review across year end?
Use the correct year for installation and count dates. The capacity-based review is January 20, 2027.
The earlier constraint may differ for another calendar limit.
How do I back up both dates used by a filter forecast?
Export JSON and compare start, count date, capacity and used amount after import. The one-hundred-day capacity estimate retains its original count-date meaning.
A restored historical count should be updated before current planning.
How do I rebuild after a new cartridge is actually installed?
Save the genuine replacement event and then rebuild. The new record starts with 600 litres of entered capacity.
The software cannot verify that a replacement physically occurred.
