Free tool
Is It Worth Stocking This Spare Part?
Enter your spare part data and get a clear recommendation — stock it, or order on demand.
Spare part data
Downtime impact
Result: spare part stocking recommendation
Want help planning your critical spare parts strategy and stock levels?
Request a spare parts strategy consultationHow the calculation works
The recommended stock is calculated as: rounded-up (failures per year × lead time in days ÷ 365), i.e. the expected number of failures during one lead time. Holding cost = part price × 15% (a typical assumption for carrying cost) × quantity. Risk cost = failures per year × lead time × 24 h × downtime cost per hour. If the risk cost exceeds the holding cost, the tool recommends keeping the part in stock; otherwise, order on demand.
Example: a part costs EUR 450, lead time 21 days, 0.5 failures a year and downtime of EUR 200/h. The recommended quantity is 1, the holding cost EUR 68 and the risk cost EUR 50,400 – so keep it in stock.
Frequently asked questions
Why is a 15% carrying cost used?
It is a common typical assumption for carrying cost (capital, space, obsolescence). For a more precise estimate, use your own company’s figures.
How do I estimate the lead time?
Ask the supplier for a realistic lead time including transport and customs, and prefer a conservative value.
What if there have been no failures before?
Use the manufacturer’s MTBF or an expert estimate. A very low frequency gives a low risk cost.
Related tools
Related services
Methodology and limitations
Methodology based on standard industry calculations and Maintest’s practical industrial experience. This tool provides a planning estimate and does not replace project-specific engineering assessment. This tool is a screening and planning aid developed by Maintest. Results are indicative and depend entirely on the figures and answers you enter. They are not an engineering calculation, a safety assessment or a substitute for the manufacturer’s instructions, applicable standards or professional judgement. Weights, benchmarks and default values are Maintest planning assumptions and can be adjusted to your situation. Do not use this tool as the only basis for safety-critical decisions such as lifting, electrical work or lockout procedures.
Tool version 1.0 · Updated October 2026
Want help planning your spare parts strategy?
Contact us — we will respond as soon as possible.