Quick answer
Selling 20 units a day with a 14-day lead time and 7 days of safety cover, reorder at 420 units: 280 to cover the lead time plus 140 of safety stock. With 500 units on hand, you reach that point in 4 days, so the order goes in this week.
How the Inventory Reorder Point works, step by step
Enter average daily unit sales, current stock on hand, supplier lead time in days, safety stock cover in days, and how many days of cover each order should buy. The calculator returns the reorder point, the days of stock you have left, the days until you hit the reorder point, and a suggested order quantity. At the defaults — 20 units a day, a 14-day lead time, 7 days of safety cover and 500 units on hand — the reorder point is 420 and the suggested order is 520 units.
The reorder point has two parts. Lead-time demand is daily sales multiplied by lead time: the stock you will sell while the next order is on its way. Safety stock is daily sales multiplied by your safety days: the buffer for demand spikes and late deliveries. Add the two together and you have the stock level that triggers an order.
Safety days are the judgement input. A product with steady sales and a reliable supplier runs fine on 3 to 5 days of cover. A product with spiky demand, a long or variable lead time, or a supplier who misses dates needs 10 to 14 days. Too much safety stock ties cash up on shelves; too little turns a late delivery into a stockout.
Lead time means order to shelf-ready, not shipping alone: supplier processing, production, transit, customs, receiving and inspection all count. A product with 5-day shipping and 9 days of production has a 14-day lead time. Underestimating lead time is the most common reason reorder points fail in practice.
The suggested order quantity covers your chosen days of cover on top of the reorder point, minus what you already hold. Recalculate whenever demand or supply changes: a promotion, a viral mention, a new supplier, a port delay. A reorder point built on last quarter's daily sales will stock you out in a growth month and overstock you in a decline.
The formula
Reorder point = (daily sales x lead time) + (daily sales x safety days). Days of stock left = current stock / daily sales. Suggested order = (daily sales x cover days) + reorder point - current stock.
Worked example — try it on the calculator above
Worked example: 20 units a day, 14-day lead time
Daily sales of 20 units and a 14-day lead time give lead-time demand of 280 units. Seven days of safety cover adds 140 units, so the reorder point is 420. With 500 units on hand you have 25 days of stock and reach the reorder point in 4 days, so the order goes in this week. For 30 days of cover per order, the suggested quantity is 600 + 420 - 500 = 520 units. Cut safety cover to 3 days and the reorder point falls to 340, freeing 80 units of cash — a fair trade only if demand is steady and the supplier delivers on time.
Frequently Asked Questions
What is safety stock and how much do I need?
Safety stock is inventory held beyond expected lead-time demand to absorb surprises: demand spikes and late deliveries. This calculator sizes it in days of cover rather than units, so it scales with sales. Start at 3 to 5 days for steady products with reliable suppliers and 10 to 14 days for volatile ones, then adjust from your stockout history: every stockout argues for more, every overstock for less.
Does lead time include production and processing?
It must include everything between deciding to order and the goods being sellable: supplier processing, production, transit, customs, receiving and inspection. Quoted '5-day shipping' on a product with 10 days of production is a 15-day lead time. Underestimating lead time is the most common cause of reorder points that fail in practice.
How often should reorder points be reviewed?
Monthly for active products, and immediately when demand or supply changes materially: a promotion, a viral mention, a supplier change, a port delay. Seasonal products need seasonal points: the correct reorder point for November is wrong for February. The calculator's days-until-reorder output is the number to watch between reviews.
What is the difference between reorder point and reorder quantity?
The reorder point is a level of stock that triggers an order. The reorder quantity is how much the order contains, set here by the days of cover you want each order to buy. Confusing the two — ordering the reorder point amount, for example — is a frequent spreadsheet error. This calculator keeps them separate: the point says when, the suggested order says how much.
Estimates, not advice. This calculator provides educational estimates based on the inputs you enter and the assumptions shown on this page. It is not financial, tax or investment advice, and it cannot see your full situation. Verify important figures against official sources, and consider a qualified professional for decisions about your own money. See our Disclaimer and Methodology.