// Insight

When a manufacturer issues a discontinuance notice, it offers one last chance to order: the last-time buy. Whatever you commit to has to carry the product for the rest of its life, because after the LTB date the factory door closes. There's no reorder button. That's what makes sizing it both the most important and the most nerve-wracking number in obsolescence planning.

The Core Calculation

At its simplest, a last-time buy has to cover total remaining demand plus the losses and uncertainty along the way. Four inputs do most of the work:

• Remaining product life × estimated annual usage (EAU) — the baseline volume you'll consume before the product itself retires
• + attrition — board-level yield loss, handling and ESD damage, and rework scrap that never make it into a finished unit
• + service and spares — field replacements and repair demand, which routinely outlast production by years
• + safety stock — a deliberate margin for forecast error, because under-shooting has no cheap remedy

The honest part of this exercise is admitting how uncertain the EAU and remaining-life numbers are. A buy sized to a confident-looking forecast that's quietly wrong is still wrong — just expensively so.

The Two Ways to Get It Wrong

Under-buy, and you're back on the secondary market within a couple of years, sourcing a now-obsolete part under time pressure — the exact scenario the last-time buy was supposed to prevent. Over-buy, and the penalty is quieter but real: capital tied up in stock that depreciates, warehouse space consumed, and — for moisture- and date-code-sensitive parts — components that can age past acceptance windows before they're ever used.

The Hidden Costs of a Big Buy

A large last-time buy looks like safety, but it carries costs that don't show up on the purchase order:

• Capital locked in inventory that won't move for years
• Storage — including ESD- and moisture-controlled conditions for sensitive devices
• Date-code aging — parts can drift past customer or internal acceptance windows (see moisture sensitivity handling)
• Your own obsolescence — if the end product is discontinued early, the surplus is stranded

Alternatives to One Giant Order

The last-time buy isn't the only instrument, and often shouldn't be the whole answer:

• Bridge buy — purchase just enough to cover a redesign, then qualify a replacement and move on
• Source later on the secondary market — let a vetted independent carry the obsolescence risk and supply as you need it, instead of warehousing a decade of stock yourself
• Blend the two — a modest last-time buy for near-term certainty, plus secondary-market sourcing for the long tail of service demand

RH Electronics works both sides of this — helping cover a last-time buy when it's the right call, and locating obsolete parts on the open market when the window has closed or a giant buy doesn't make sense. Search our catalog or submit a requirement.