Quick guide
How to use this calculator
- Gather Cohort A units, Cohort A age (days), Cohort B units, and Cohort B age (days) for the same business scenario before calculating.
- Keep units and time bases aligned: daily demand needs lead time in days, and item costs must match the quantity represented by one inventory unit.
- Apply the displayed inventory aging result to the stated decision only after checking every entered assumption.
Calculation method
Calculation method
Weighted age = (units A × age A + units B × age B) ÷ total units.
The calculation uses these named inputs: Cohort A units, Cohort A age (days), Cohort B units, and Cohort B age (days). No market rate, benchmark, tax rule, or accounting classification is inserted automatically.
Fixed-decimal arithmetic remains exact through display unless a result is explicitly labelled approximate, such as a square-root inventory quantity.
Inventory planning and replenishment
Where the Inventory Aging Calculator helps
Calculate a weighted average inventory age for two entered stock cohorts.
Use the result to translate entered demand, lead time, order cost, holding cost, and service assumptions into a planning quantity or interval.
- Prepare a purchase-order scenario
- Stress-test a supplier lead-time change
- Compare ordering and holding-cost assumptions
Interpretation check
How to audit the result
Recalculate the scenario when any of these inputs changes: Cohort A units, Cohort A age (days), Cohort B units, and Cohort B age (days).
Keep this formula beside the result: Weighted age = (units A × age A + units B × age B) ÷ total units. Then compare the output with the source records and the calculator-specific assumption below.
- Confirm that all amounts use one currency and reporting period.
- Check that rates, counts, and quantities describe the same population or transaction set.
- Save the entered assumptions with the decision; the result alone is not reproducible evidence.
Worked example
Worked example
100 units aged 30 days and 50 units aged 90 days have a weighted average age of 50 days.
Weighted age = (units A × age A + units B × age B) ÷ total units.
Supported inputs
Precision and limits
Visible input limits
Fixed decimals accept up to 30 digits and 12 decimal places and are capped at an absolute value of 1e12 per input. Rates are capped at 1000%; percentage shares and method-specific domains may be narrower.
International scope
No currency, tax jurisdiction, accounting framework, payroll rule, marketplace fee schedule, financing term, or industry benchmark is selected automatically.
Decision boundary
Use the result to translate entered demand, lead time, order cost, holding cost, and service assumptions into a planning quantity or interval. Results remain arithmetic scenarios, not accounting records, forecasts, valuations, legal interpretations, professional advice, or recommendations.
Calculator-specific assumptions
This is a scenario from visitor-entered values. Keep currencies, periods, accounting classifications, and operating definitions consistent. It is not accounting, tax, legal, investment, or business advice.