Last time buy: how to plan and calculate the right quantity
By Mark Tomasi, Managing DirectorLast updated
In short
A last time buy (LTB) is your final chance to order a discontinued component from the manufacturer. Getting the quantity right means adding up remaining production and service demand, allowing for scrap and a safety buffer, and subtracting stock you already hold. Missed the date? Distributor stock and the open market are the remaining options.
What is a last time buy?
When a manufacturer discontinues a component, it issues a discontinuation notice (PDN, often called an EOL notice) with a final date for orders. A last time buy is the order you place before that date to cover all your remaining need for the part — for production, service and repairs.
Last time buy orders are normally non-cancellable and non-returnable (NCNR). Whatever you order, you own. That is why the quantity decision matters more than for any ordinary purchase.
The last time buy timeline
| Milestone | What happens | Typical timing |
|---|---|---|
| Notice issued | The manufacturer announces the discontinuation and lists the affected part numbers | Day 0 |
| Last time buy date | Final day to place orders, usually NCNR | Commonly at least 6 months after the notice |
| Last time ship date | Final deliveries from the manufacturer | Commonly at least 12 months after the notice |
| After last time ship | Only remaining distributor stock, aftermarket production or the open market | — |
Don't wait for the deadline
Demand often peaks in the last weeks before the last time buy date, and manufacturers may cap quantities. Place the order as soon as the numbers are agreed.
How to calculate the last time buy quantity
Work through the demand in five steps:
- Production demand: forecast units per year × remaining years of production (or until a redesign is ready) × parts per unit.
- Service demand: spare parts, repairs and warranty for the installed base — often forgotten, and often years longer than production.
- Scrap and yield loss: add your typical attrition in assembly and test, commonly a few percent.
- Safety buffer: add a margin for forecast uncertainty, sized to how much a shortfall would cost you.
- Stock on hand: subtract what you, your EMS provider or other sites already hold — then round up to the manufacturer's order multiple (reel, tray or tube).
As a formula: LTB quantity = (production demand + service demand) × (1 + scrap rate) + safety buffer − stock on hand.
| Step | Example |
|---|---|
| Production: 2,000 units per year × 5 years × 1 part per unit | 10,000 |
| Service and repairs: 5% of production | + 500 |
| Scrap: 2% | + 210 |
| Safety buffer: about 5% | + 535 |
| Stock on hand | − 1,800 |
| Net requirement | 9,445 |
| Rounded up to reels of 2,500 | 10,000 |
Weighing the cost of buying too much against too little
A last time buy ties up capital in stock that must be stored, insured and may never be used if demand falls. Buying too little can be far more expensive: a stopped production line, open-market prices for the missing parts, or a redesign earlier than planned.
Compare the two honestly. For a low-cost part in a product with a long service life, buying generously is usually cheaper than running out. For an expensive part with uncertain demand, a smaller last time buy combined with a planned redesign may be the better choice.
If you end up with more than you need, the surplus still has value — see how to sell excess components.
Storing last time buy stock
Parts bought for five or ten years of use must stay solderable and undamaged for that long.
- Keep parts in their original, sealed packaging with labels and documentation — it preserves traceability and value.
- Control moisture: moisture-sensitive parts must be stored and handled according to their MSL rating (J-STD-033), in dry packs or dry cabinets.
- Control temperature, humidity and ESD in the storage area.
- For very long storage periods, follow IEC 62435, the standard for long-term storage of electronic semiconductor devices, or use a specialised storage provider.
- Check solderability before using parts that have been stored for many years.
OEM or EMS: who places the order?
When production is outsourced, the EMS provider often places the last time buy on the OEM's behalf. Because the order is NCNR, agree in writing who owns the stock, who pays for it and where it is stored — before the order is placed, not when the stock needs to be used.
Missed the last time buy date?
Once the manufacturer's window has closed, there are still options:
- Authorised distributors may hold remaining stock for months after the last time ship date.
- Some parts continue in production under licence from an authorised aftermarket manufacturer.
- The open market — brokers, independent distributors and OEM excess stock — is often the only remaining source for older parts.
Open-market parts carry counterfeit and quality risk, so the supplier's inspection matters.
How Emporra handles it
Every part we ship is inspected before shipment to a published counterfeit-avoidance standard — IDEA-STD-1010-B or SAE AS6171 — and arrives with a written inspection report. Deeper analysis is available on request. Read how our inspection works.
Send us the part number and quantity and we'll search our vetted global supplier network and come back with sourcing options within one business day. For the wider picture, see our obsolescence management guide.