Last Time Buy Quantity Calculator
When a supplier announces end of life, you get one chance to buy. This calculator estimates how many parts to buy to cover your support period, what that costs and what holding that stock will cost, so the decision can be compared with a redesign.
Your numbers
Average yearly usage across production and service.
How long you must keep building or repairing the product.
Expected process loss across the period.
Safety margin for demand growth and repair stock.
Capital, storage, insurance and obsolescence risk per year.
Your results
Simplified model with flat demand. Real last time buy decisions should also consider forecast changes, redesign cost, shelf life, counterfeit risk and supplier buyback terms.
Last time buy quantity vs years of support
Sweeps Years of support needed from 1 to 15, holding your other inputs fixed.
Spot end-of-life parts earlier
Optional: ask how supplier notices and ERP usage could be combined into an early warning view.
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How to use it
Enter your average yearly demand across production and service, the number of years you must support the product, and your losses and spares. Add current stock and open orders. The calculator subtracts what you already have and rounds the shortfall up to the minimum order quantity. Compare the investment and carrying cost to the cost of redesigning or qualifying a substitute.
The formula
Requirement equals annual demand times years times one plus scrap times one plus spares. Shortfall is requirement minus stock minus open orders, and the buy is the shortfall rounded up to a multiple of the minimum order quantity. Carrying cost uses the average inventory over the period, which is why the final term is divided by two.
- Demand should include service and repair needs, not only new builds.
- Use forecast demand when you expect strong growth or decline.
- Shelf life limits how long some parts can actually be stored.
Reading the result
If the investment is small compared to a redesign, the last time buy is usually the practical choice. If years of cover exceeds the realistic product life, you may be over-buying. Test lower years and spares to see how sensitive the quantity is, and use the chart to see the effect of longer support commitments.
Common mistakes
Ignoring service demand, buying only for the current forecast when a contract requires many more years, and forgetting storage conditions such as moisture control for semiconductors are the main errors. Always confirm with the supplier if a buyback or extended support programme exists.
Frequently Asked Questions
What is a last time buy?
A final purchase of a part before the manufacturer stops producing it, sized to cover the expected future demand of your product until a replacement, redesign or end of support.
How much spares allowance should I add?
It depends on forecast uncertainty and consequences of a stockout. Ten percent is a common starting point, but long-life defense or medical programs may justify more, balanced against carrying cost.
Should I buy more than the calculated quantity?
Consider it only if the cost of running out is high and shelf life allows. Larger buys tie up cash and risk write-off if the program ends early.
Does the calculator account for price breaks?
No. Enter the unit cost you expect at the final quantity, or run it twice with different prices and compare.
We can help pull real demand, stock and supplier notice data from your ERP into a read-only obsolescence view.
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