Reorder Point Calculator

Days of cover is one division, and this keeps it one

What is on hand, divided by what goes out in a day. That is how long the line lasts.

Take the supplier’s lead time off it and you have how long you have got before the order needs to leave. That is the whole calculation, and it is the calculation that actually runs a shelf.

Every product sold into this space wraps that division in something else — a model, a seasonality curve, a smoothing factor, a recommendation. This does not. It is a division, printed, with the two numbers that went into it visible beside the answer.

It reads your spreadsheet and shows you what it thinks the columns mean

Drop the file straight onto the page. It looks at your own headers and guesses which column is the part, which is the quantity, which is the usage.

Then it shows you the guess.

That display is the feature. A tool that matched the wrong column silently would do confident arithmetic on the wrong number, and confident arithmetic on the wrong number is the failure that ends in a shelf full of the thing you already had. Showing the match means a wrong guess costs you four seconds instead of a purchase order.

Three numbers are yours and none of them has a default

How many days your usage figure covers. A usage number is meaningless until you say what window it came from. Thirty days and ninety days give very different answers, and only you know which one you pulled.

How much buffer you want on top. This starts at zero, deliberately. A safety margin nobody chose is a number the page invented, and it would sit inside every answer afterwards without anybody remembering it was there.

How far ahead you order for. Weekly, monthly, to the next visit from the rep. That is about your cash and your storage.

What it will not tell you, and this one matters

It will never state the date you run out.

It will tell you how many days of cover you have and how many of those are already spoken for by the lead time. It will not turn that into a date on a calendar, because a date is a promise about the future and this is a division of two numbers you typed.

The difference sounds like hair-splitting until somebody schedules around the date and the usage changes. Then it is the difference between a tool that told you something true and one that told you something that felt more useful.

It forecasts nothing, fits no curve and smooths nothing. If your usage figure is wrong, the answer is wrong in exactly the way your figure is wrong, which is a property you can reason about. A smoothed answer is wrong in a way nobody can reason about.

What it replaces

The reorder that happens by walking the aisle and noticing gaps. Or the spreadsheet with a formula in it that was right in 2021, has a hardcoded lead time somewhere, and gets copied forward every month.

You set your three numbers once. Every run after that is dropping this month’s file on the page.

Who it is for

Retail, chandlery, parts counters, anywhere with a shelf that has to be there when somebody asks for it — and where the buying decisions are made by somebody who knows the trade rather than by a system.

What it will not do

It invents no safety stock. The buffer is zero until you set it.

It suggests no reorder point. What yours should be depends on your supplier’s reliability, your storage and what it costs you to be out of that line for a day. It applies the numbers you set.

It compares you to nothing. No category norms, no seasonal patterns, nothing from outside your own file.

Nothing you drop on the page is sent anywhere. The file is read in your browser and never uploaded. Your usage data is a picture of your business, and it stays on the machine you opened it on. Close the tab and it is gone.