# Last Time Buy Quantity Calculator

> Source: https://netray.co/tools/last-time-buy-quantity-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Calculate the last time buy quantity and the investment and carrying cost for a part reaching end of life.

## Category

engineering-plm

## Industry

Electronics Manufacturing

## Audience

- Engineering manager
- Buyer
- Component engineer

## Tool

**Kind:** calculator

**Currency:** $

**Inputs:**

#### Average annual demand

**Key:** annual_demand

**Type:** number

**Default:** 4000

**Min:** 0

**Step:** 100

**Unit:** units

**Help:** Average yearly usage across production and service.

#### Years of support needed

**Key:** years

**Type:** number

**Default:** 7

**Min:** 0

**Step:** 1

**Unit:** years

**Help:** How long you must keep building or repairing the product.

#### Scrap and handling loss

**Key:** scrap

**Type:** number

**Default:** 2

**Min:** 0

**Step:** 0.5

**Unit:** %

**Help:** Expected process loss across the period.

#### Extra spares allowance

**Key:** spares

**Type:** number

**Default:** 10

**Min:** 0

**Step:** 1

**Unit:** %

**Help:** Safety margin for demand growth and repair stock.

#### Stock on hand

**Key:** onhand

**Type:** number

**Default:** 1500

**Min:** 0

**Step:** 100

**Unit:** units

#### Open orders

**Key:** onorder

**Type:** number

**Default:** 500

**Min:** 0

**Step:** 100

**Unit:** units

#### Minimum order quantity

**Key:** moq

**Type:** number

**Default:** 250

**Min:** 1

**Step:** 50

**Unit:** units

#### Unit cost

**Key:** cost

**Type:** number

**Default:** 3.2

**Min:** 0

**Step:** 0.1

**Unit:** $

#### Annual carrying cost

**Key:** carry

**Type:** number

**Default:** 20

**Min:** 0

**Step:** 1

**Unit:** %

**Help:** Capital, storage, insurance and obsolescence risk per year.

**Outputs:**

#### Total requirement

**Key:** required

**Expr:** annual_demand * years * (1 + scrap / 100) * (1 + spares / 100)

**Format:** integer

**Description:** Demand over the support period including losses and spares.

#### Shortfall after stock and orders

**Key:** gap

**Expr:** max(0, required - onhand - onorder)

**Format:** integer

#### Last time buy quantity

**Key:** buy

**Expr:** if(gt(gap, 0), ceil(gap / moq) * moq, 0)

**Format:** integer

**Primary:** true

**Description:** Shortfall rounded up to the minimum order quantity.

#### Purchase investment

**Key:** invest

**Expr:** buy * cost

**Format:** currency

**Primary:** true

#### Estimated carrying cost over period

**Key:** carry_cost

**Expr:** (buy + onhand + onorder) * cost * carry / 100 * years / 2

**Format:** currency

**Description:** Assumes inventory declines roughly linearly to zero.

#### Years of cover after purchase

**Key:** cover

**Expr:** if(gt(annual_demand, 0), (onhand + onorder + buy) / (annual_demand * (1 + scrap / 100) * (1 + spares / 100)), 0)

**Format:** years

**Chart:**

#### Last time buy quantity vs years of support

**Type:** line

**X:** years

**From:** 1

**To:** 15

**Steps:** 15

**Series:**

- buy

**Disclaimer:** 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.

## Content

**Intro:** 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.

**Sections:**

#### How to use it

**Body:** 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

**Body:** 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.

**Bullets:**

- 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

**Body:** 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

**Body:** 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.

**Cta:** We can help pull real demand, stock and supplier notice data from your ERP into a read-only obsolescence view.

**Faq:**

#### What is a last time buy?

**Answer:** 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?

**Answer:** 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?

**Answer:** 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?

**Answer:** No. Enter the unit cost you expect at the final quantity, or run it twice with different prices and compare.

## Search terms

last time buy calculator, LTB quantity calculation, end of life buy calculator, component obsolescence last time buy, EOL buy quantity formula, last buy quantity excel, lifetime buy calculator

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