How do you calculate protected days of supply?

Divide committed coverage plus the safety buffer by daily demand, against the replenishment lead time. In the example the inputs yield about 12.83 protected days of supply versus 14.12 unprotected days.

What is a good level of lead-time coverage?

Protected days should at least span your replenishment lead time. Here 12.83 protected days against the lead time signals coverage is slightly short — worth adding buffer before a change order hits.

Why separate protected from unprotected days?

Protected days include your safety buffer; unprotected days (14.12 here) are the raw demand-coverage figure. The gap shows how much the buffer extends or fails to extend your runway.

How big should the schedule-change buffer be?

Size it to the largest realistic late opening release or change order you face. On change-prone custom jobs a buffer of one to two days of demand is common, which is why the safety factor input exists.

What happens if lead time exceeds protected days?

You risk a stockout on custom openings mid-project. When protected days fall below replenishment lead time, release the next custom order earlier or widen the buffer.

Custom order lead time vs. standard catalog lead time?

Custom openings carry longer, more variable lead times than catalog hardware, so they need explicit coverage math. Catalog items can lean on standing stock instead.

Doors, Hardware & Access Control Manufacturing calculator

Custom Order Lead Time Calculator

Custom order lead-time coverage tells a door and hardware planner how many days of demand their current commitment protects against, given the replenishment lead time and a safety buffer for schedule changes. Materials planners and project managers use it on custom openings where lead times are long and change orders are common. Custom hardware sets rarely sit in finished stock, so the calculation works in committed coverage rather than shelf inventory. Knowing protected days keeps a job from stalling when a GC slides a schedule or adds openings late.

What this calculator does

Estimate required inventory or order coverage for custom doors, frames, hardware sets, cylinders, finish options, or access-control components with long lead times.
Use it when custom order lead time in doors, hardware and access control manufacturing is being sized for a buffer or safety stock review.
It converts on-hand or committed coverage and a schedule-change buffer into protected days of supply against daily custom demand at a known replenishment lead time.

Formula used

Lead-time demand coverage = daily custom opening or hardware demand × custom order replenishment lead time
Required custom order coverage = lead-time demand coverage + schedule-change safety buffer

Inputs explained

Daily custom opening or hardware demand:
Custom order replenishment lead time:
Schedule-change safety buffer:

How to use the result

Use it when planning custom opening releases, sizing buffers for change-prone projects, or judging whether current coverage spans the lead time.
It assumes steady daily demand; custom door work is lumpy by nature, so a single large opening release can consume coverage far faster than the average day implies.

Current U.S. benchmarks

U.S. housing starts run at 1,177k per year (Census, May 2026), down 8.7% from a year earlier, the demand driver for building products.
Steel mill PPI stands at 348.53 (BLS, May 2026), up 6.7% from a year earlier. New factory orders are up 2.3% year over year (Census).

Common questions

How do you calculate protected days of supply? Divide committed coverage plus the safety buffer by daily demand, against the replenishment lead time. In the example the inputs yield about 12.83 protected days of supply versus 14.12 unprotected days.
What is a good level of lead-time coverage? Protected days should at least span your replenishment lead time. Here 12.83 protected days against the lead time signals coverage is slightly short — worth adding buffer before a change order hits.
Why separate protected from unprotected days? Protected days include your safety buffer; unprotected days (14.12 here) are the raw demand-coverage figure. The gap shows how much the buffer extends or fails to extend your runway.
How big should the schedule-change buffer be? Size it to the largest realistic late opening release or change order you face. On change-prone custom jobs a buffer of one to two days of demand is common, which is why the safety factor input exists.
What happens if lead time exceeds protected days? You risk a stockout on custom openings mid-project. When protected days fall below replenishment lead time, release the next custom order earlier or widen the buffer.

Last reviewed 2026-05-12.