Free tool
Demand forecast simulator
A demand forecast projects your current stock forward at your current sales rate, adjusted for growth, and shows the day you cross your reorder point. Start with 500 units selling 10 a day, growing 5% a month, with a 14 day lead time and 7 day buffer, and you reorder around day 29.
Demand forecast simulator
How to use it
- Enter today's stock and sales rate. Take the units on hand right now and the average units sold per day over a recent window. These two set where the projection starts and how quickly it falls.
- Set a monthly growth rate. Enter the percentage you expect sales to grow each month. It compounds daily across the 90 days. A negative number models a product whose demand is easing off after a peak.
- Add your lead time and safety days. Together these set the reorder point the projection is measured against. Because the sales rate grows, the reorder point rises with it rather than sitting at a fixed level.
- Read the reorder day and the 30, 60 and 90 day stock. The chart shows projected on-hand stock across 90 days, with a dashed line at the reorder point and a marker on the day the projection crosses it. That day is when to place the order.
Every term used here is defined in the inventory planning glossary, and the arithmetic behind all of it is worked through on how inventory forecasting works.
Questions merchants ask
How does the simulator project demand?
It converts your monthly growth percentage into a daily compounding factor, then walks day by day for 90 days: it works out that day's sales rate, subtracts it from stock, and checks whether stock has fallen to that day's reorder point. Stock is floored at zero rather than going negative.
Why does the reorder point move over the 90 days?
Because it is calculated from that day's sales rate, not from today's. If sales are growing, the units you will sell during a fixed lead time grow with them, so the level at which you need to reorder rises too. A fixed threshold on a growing product triggers too late.
What if there is no reorder day in the 90 day window?
Then your current stock covers the whole window at the rate you entered, and the simulator says so instead of inventing a date. It is worth re-running as demand shifts, because a growth rate that looked modest compounds noticeably over a quarter.
How accurate is a straight-line growth forecast?
It is a projection, not a prediction. A single growth rate cannot know about a promotion you have planned, a supply delay, or a seasonal peak. It is useful for seeing roughly when a reorder is due and for testing how much a change in growth or lead time moves that date.
A forecast per product, from your own sales
Replinish reads up to 365 days of Shopify order history, forecasts each product separately, and recomputes overnight as new orders come in.
Launching on the Shopify App Store shortly. Tell us your store and we'll let you know when you can install it. Plans are billed by Shopify, and you pick one in your Shopify admin after installing.