JIT Manufacturing Reorder Window
Reverse-calc the latest purchase-order release day based on supplier lead time.
These calculators are for informational purposes only and do not constitute legal, financial, or professional advice.
How the JIT Manufacturing Reorder Window works
The JIT Manufacturing Reorder Window works backward from the day you need stock on the floor to the last day you can safely release the purchase order. Enter the required-by date — the day a line would otherwise go down — and the supplier lead time in business days, and it subtracts that lead time across working days to return the latest release date that still lands the parts on time.
Counting the lead time in business days rather than calendar days is the point. Suppliers quote "ten days" but their plants, freight forwarders, and your own receiving dock run on weekdays, so a ten-day lead time dropped onto a raw calendar can land you short by a full weekend or a public holiday. The reverse calculation skips weekends and the holidays for the calendar you select, so the release date reflects days work actually happens.
In just-in-time production the release date is a knife edge: order earlier and you carry inventory the JIT model is designed to eliminate; order later and you risk a line-down event that costs far more than the parts. Projecting the latest defensible release day — and a checkpoint a little ahead of it — gives planners a clear trigger date instead of a gut feel.
Worked example
A subassembly is needed on the line by Friday October 30, and the supplier quotes an eight-business-day lead time. Counting eight business days backward from October 30 — skipping two weekends — puts the latest safe purchase-order release on Tuesday October 20. Release on the 20th and the parts arrive just in time; slip to the 21st and, once the weekend is counted, the line is short.
Frequently asked questions
Is the lead time counted in business days or calendar days?
Business days. The calculator subtracts the supplier lead time across working days only, skipping weekends and the public holidays for the country you choose, because production, freight, and receiving all run on business days. Entering a supplier quote that was given in calendar days will make the release date too late, so convert it first.
Whose holiday calendar should I select?
Use the calendar that governs the critical part of the chain — usually the supplier plant and the transit lane feeding your dock. A lead time that spans the supplier country's national holiday loses those days of progress, so selecting the right calendar keeps the release date honest.
Why release on the latest safe date instead of earlier?
Because holding inventory is the cost just-in-time exists to remove. The latest safe release date is the trigger that keeps parts flowing without building a buffer on the floor — but treat it as a floor, not a target, and release a touch earlier when the lead time itself is unreliable.
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