How do you calculate VMI days of supply?

Divide on-hand stock by daily usage, then divide by the safety multiplier. With 4,500 units on hand, 300 units/day usage, and a 1.2x multiplier, that is 4,500 ÷ 300 ÷ 1.2 = 12.5 protected days.

What's the difference between protected and unprotected days?

Unprotected days is raw cover — 4,500 ÷ 300 = 15 days. Protected days applies the 1.2x buffer to leave 12.5 days, the number you should actually trigger reorders on.

What is a good safety multiplier for VMI?

1.1x-1.3x is common for stable, short-lead-time items; 1.5x or higher is used where demand is volatile or the supplier's replenishment cycle is long or unreliable.

When should the supplier trigger a top-up?

When protected days fall to or below the supplier's replenishment lead time plus a review interval. If a rep visits weekly and lead time is 3 days, 12.5 protected days is comfortable; under about 10 it gets tight.

Why divide by the multiplier instead of multiplying safety stock?

Dividing raw cover by the multiplier is a quick way to discount available days for uncertainty — it shrinks 15 raw days to 12.5 planning days without needing a separate safety-stock unit calculation.

Does this account for in-transit replenishment?

No. It only reflects stock physically in the bin. If a top-up is already on the way, add those in-transit units to on-hand before running the number.

Supply Chain & Procurement calculator

Vendor Managed Inventory Days Calculator

Vendor managed inventory (VMI) days tells you how many days of production the current bin stock will cover once you apply a safety multiplier to hedge against demand spikes and replenishment lag. Supply planners and VMI suppliers use it to decide when a rep needs to top up a customer-owned bin before a line-down risk appears. It matters because in a VMI model the supplier owns the replenishment decision, so a mis-read on days-of-cover shows up as either a stockout on the customer's line or working capital tied up in overstock. The safety multiplier is what separates the raw 'unprotected' cover from the number you actually plan reorders against.

What this calculator does

Estimate VMI coverage from vendor stock, daily usage, and policy factor.
Use it when vendor managed inventory days in supply chain and procurement is being sized for a buffer or safety stock review.
It converts on-hand stock and daily usage into protected days of supply by dividing raw cover by a safety multiplier.

Formula used

Protected days = inventory on hand ÷ daily usage ÷ safety multiplier

Inputs explained

On-hand stock at the VMI bin:
Average daily consumption:
Buffer safety multiplier:

How to use the result

Use it on VMI bin walks and replenishment reviews to decide whether a top-up is needed before the next supplier visit.
It assumes steady daily usage; lumpy or seasonal demand can burn through the buffer far faster than a flat average suggests.

Current U.S. benchmarks

U.S. manufacturing runs at 75.6% of capacity (Federal Reserve, May 2026). New factory orders are up 2.3% year over year (Census).
Sourcing currencies as of 2026-07-02 (Federal Reserve H.10): 6.7886 CNY and 17.4524 MXN per USD. Landed-cost comparisons move with these daily rates.
U.S. iron and steel imports ran $2.1B in May 2026 (Census International Trade). The U.S. ran a trade deficit of $0.4B in the category that month. Import volumes are the pressure gauge behind tariff and reshoring decisions.

Common questions

How do you calculate VMI days of supply? Divide on-hand stock by daily usage, then divide by the safety multiplier. With 4,500 units on hand, 300 units/day usage, and a 1.2x multiplier, that is 4,500 ÷ 300 ÷ 1.2 = 12.5 protected days.
What's the difference between protected and unprotected days? Unprotected days is raw cover — 4,500 ÷ 300 = 15 days. Protected days applies the 1.2x buffer to leave 12.5 days, the number you should actually trigger reorders on.
What is a good safety multiplier for VMI? 1.1x-1.3x is common for stable, short-lead-time items; 1.5x or higher is used where demand is volatile or the supplier's replenishment cycle is long or unreliable.
When should the supplier trigger a top-up? When protected days fall to or below the supplier's replenishment lead time plus a review interval. If a rep visits weekly and lead time is 3 days, 12.5 protected days is comfortable; under about 10 it gets tight.
Why divide by the multiplier instead of multiplying safety stock? Dividing raw cover by the multiplier is a quick way to discount available days for uncertainty — it shrinks 15 raw days to 12.5 planning days without needing a separate safety-stock unit calculation.

Last reviewed 2026-05-12.