FIFO Inventory Deduction Explained: Why Factories Lose Material Without It

FIFO — first-in, first-out — sounds like an accounting concept. In a factory, it's an operational one with real material and money on the line. When inventory deduction doesn't follow FIFO, the leakage shows up as wrong batch costs, expired stock that nobody noticed, and a slow drift between what your books say and what's actually on the shelf.

What FIFO Actually Means in Production

When a work order consumes raw material, FIFO says: deduct from the oldest stock first. If you received 100 kg of steel on Monday at ₹80/kg and 100 kg on Friday at ₹85/kg, today's consumption draws from Monday's lot until it's exhausted. Simple in concept, surprisingly painful to enforce in practice without software.

Why It Matters for Batch Costing

If your system deducts at a flat average or grabs from whichever lot is convenient, the cost recorded against each batch is fiction. A batch that actually consumed ₹80 steel gets costed at ₹82.50 (the average). Margins look off. Pricing decisions get made on wrong data. Multiply that across a thousand batches a year and the cumulative distortion is meaningful.

Why It Matters for Material Health

Materials degrade. Steel rusts, rubber hardens, chemicals expire. FIFO ensures the oldest material moves first — which is exactly what you want for materials with limited shelf life. Without it, last week's delivery quietly sits at the back of the shelf until somebody finds it three months later, unusable.

The Spreadsheet Failure Mode

In a spreadsheet, FIFO requires lot-level tracking, manual matching of consumption to lots, and recalculation every time stock moves. Nobody actually does this — what factories do instead is record consumption against a single SKU at an average cost, and call it good enough. It's not good enough. It's just invisible.

What Proper FIFO Deduction Looks Like

In a system built for it, every receipt creates a lot record with its own cost and date. Every consumption automatically pulls from the oldest available lot. The batch cost is the actual cost of what was actually consumed — not an average, not a guess. Stock counts at the end of the month match what's on the shelf because the math has been honest the whole time. FIFO done properly isn't an accounting nicety. It's the difference between knowing your margins and hoping you do.