FIFO inventory calculator

First-in first-out inventory costing answers a close-period question that a single merchandising identity cannot: given the purchase lots still on the shelf and the units that left, what is ending inventory worth, and what is cost of goods sold? FIFO treats the oldest units as sold first, so remaining stock is valued at the newest unit costs. This FIFO inventory calculator accepts an ordered list of purchase batches — units and unit cost per lot, oldest first — plus units sold, consumes those units from the front of the queue, and returns both ending inventory value and cost of goods sold.

How FIFO costing turns purchase lots into COGS and ending inventory

First-in first-out is a cost-flow assumption, not a warehouse map. You send purchase batches in chronological order, oldest lot first: each row is a quantity of units bought at a stated unit cost. Opening stock is simply the first batch if those units arrived last period and are still on the books; there is no separate beginning-inventory field and no date stamp, because the engine never reads a clock.

Units sold are then peeled off the oldest remaining lots until the sold quantity is satisfied. Cost of goods sold is the sum of units taken from each consumed lot times that lot's unit cost. Ending inventory is the sum of units still sitting in later lots times those lots' unit costs.

The two figures add back to goods available — the total cost of every unit you started with — which is the same identity merchandising books use, except here both sides are derived from lots rather than from a plugged cost-of-goods-sold line. A textbook walk-through: one hundred units at ten, then fifty units at twelve, and one hundred twenty units sold.

FIFO takes the entire first lot (one thousand of cost) and twenty units from the second lot (two hundred forty), so cost of goods sold is one thousand two hundred forty and ending inventory is the leftover thirty units at twelve, or three hundred sixty. If units sold equal units available, ending inventory is zero and every lot is consumed. If units sold are zero, cost of goods sold is zero and ending inventory equals goods available.

What this calculator does not do is sort lots by a calendar date, apply last-in first-out, compute a weighted-average unit cost, convert currencies, or reconstruct the three-line identity beginning inventory plus net purchases minus cost of goods sold. Send the lots already ordered; the engine only walks them from the front and returns both values.

Where a FIFO inventory calculator earns its keep

Controllers and bookkeepers use a FIFO inventory calculator at close to turn the period's purchase lots and units sold into the two figures the income statement and the balance sheet both need: cost of goods sold and ending inventory under the first-in first-out cost-flow assumption their policy already names. Tax pack workpapers in jurisdictions that require or permit FIFO need the same walk pinned, not a spreadsheet that silently resorted the lots.

Auditors and lenders drop the same batches into a working paper so a closing-stock number that does not follow from the oldest lots is visible before it is signed off. Merchandisers who buy in rising markets use FIFO because remaining stock is valued at newer, typically higher unit costs, and they want that valuation without rebuilding a perpetual inventory engine.

This is a different search and a different job from the merchandising identity that subtracts a given cost of goods sold from beginning inventory plus net purchases, from days inventory outstanding, from inventory turnover, and from a physical count: those tools start from different inputs and answer different questions. Failed validation does not consume balance.

Keep lots in first-in order, keep units sold within units on hand, pin the rounded figures in tests, and you get a reproducible FIFO close for checklists, classroom oracles, and edge workers without standing up a warehouse engine of your own.