How do you calculate days of inventory coverage?

Cycle stock is 81,000 units across the 90-day lead time, and the 1.1 safety multiplier brings the required position to 89,100 units. Compare that against stock on hand plus anything already on order to see whether the next cycle is covered.

What is the difference between cycle stock and the required buffer?

Cycle stock is what the 90-day lead time consumes on its own: 81,000 units. The required buffer adds the safety cushion on top, 89,100 units here, so a normal run of demand does not empty the shelf before replenishment lands.

What is a good days-of-supply for rare earth magnets?

Cycle stock is 81,000 units across the 90-day lead time, and the 1.1 safety multiplier brings the required position to 89,100 units. Compare that against stock on hand plus anything already on order to see whether the next cycle is covered.

How does lead time factor into coverage?

Lead time is the gap you must survive between reorder and receipt. Coverage below lead time means a line stoppage is likely if you reorder late, so target coverage above lead time plus buffer.

Why include a safety stock multiplier?

Demand and lead time vary. The safety factor trims the headline days to a conservative, dependable figure so you plan against a number you can trust, not a best case.

How should the required stock be used?

Increase on-hand inventory, reduce daily usage, or shorten lead time. Since single-source rare-earth lead times are hard to cut, buyers usually lift on-hand stock or qualify a second source.

Rare Earth Magnet & Motor Materials calculator

Inventory Coverage Calculator

Inventory coverage tells a magnet or motor-materials buyer how many days of production their on-hand stock of rare earth magnets will actually protect, given daily consumption, supplier lead time, and a safety-stock cushion. Supply-chain planners rely on it because rare-earth sourcing is concentrated and lead times can swing hard, so running short means idling a motor assembly line waiting on offshore replenishment. That comparison is what tells you whether your buffer is genuinely safe or dangerously thin.

What this calculator does

Estimate inventory coverage for rare earth magnet and motor materials using production-ready inputs so teams can plan replenishment and safety stock using actual usage and lead time.
Use it when inventory coverage in rare earth magnet and motor materials is being sized for a buffer or safety stock review.
It sizes the stock a replenishment cycle requires: daily usage across the lead time, then the safety cushion on top. Here that is 81,000 units of cycle stock and 89,100 units required in total.

Formula used

Inventory coverage cycle stock = inventory coverage daily usage × inventory coverage lead time
Required inventory coverage inventory = cycle stock + inventory coverage safety stock

Inputs explained

Magnet consumption per day:
Supplier replenishment lead time:
Safety stock multiplier:

How to use the result

Use it when setting reorder points or reviewing exposure on long-lead, single-source rare earth magnet inventory.
Inventory Coverage sizes the stock a replenishment cycle requires, combining cycle stock across the lead time with a safety cushion.

Current U.S. benchmarks

The producer price index for copper and brass mill shapes stands at 542.853 (BLS, Jul 2026), up 52.8% from a year earlier. Quotes priced off last quarter's material cost miss this move. Global copper trades at $13,543 per tonne (IMF via FRED, Jul 2026).
The U.S. has 5,397 electrical equipment and appliances establishments employing about 369,437 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate days of inventory coverage? Cycle stock is 81,000 units across the 90-day lead time, and the 1.1 safety multiplier brings the required position to 89,100 units. Compare that against stock on hand plus anything already on order to see whether the next cycle is covered.
What is the difference between cycle stock and the required buffer? Cycle stock is what the 90-day lead time consumes on its own: 81,000 units. The required buffer adds the safety cushion on top, 89,100 units here, so a normal run of demand does not empty the shelf before replenishment lands.
What is a good days-of-supply for rare earth magnets? Cycle stock is 81,000 units across the 90-day lead time, and the 1.1 safety multiplier brings the required position to 89,100 units. Compare that against stock on hand plus anything already on order to see whether the next cycle is covered.
How does lead time factor into coverage? Lead time is the gap you must survive between reorder and receipt. Coverage below lead time means a line stoppage is likely if you reorder late, so target coverage above lead time plus buffer.
Why include a safety stock multiplier? Demand and lead time vary. The safety factor trims the headline days to a conservative, dependable figure so you plan against a number you can trust, not a best case.

Last reviewed 2026-08-13.