Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Reorder point
920
Expected demand during lead time
770
Days of coverage per reorder
68
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How to use this
- 1Enter average daily sales (units).
- 2Enter supplier lead time (days).
- 3Enter safety stock (units).
- 4Enter typical reorder quantity (units).
- 5Read your reorder point on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Reorder point tells you exactly how many units you should have on hand when you place a new purchase order, so the replenishment arrives before you run out, accounting for both average demand during the lead time and a safety buffer for demand spikes or shipping delays. Getting this wrong in either direction is expensive: too low and you stock out and lose sales; too high and you tie up cash in excess inventory sitting in a warehouse. This calculator takes your average daily sales velocity, supplier lead time in days, and a safety stock buffer, and computes the exact unit count at which you should trigger reordering. Enter average daily units sold, lead time in days from order to received inventory, and safety stock units (calculated separately or estimated). The output shows your reorder point and, given a specified order quantity, roughly how many days of coverage that order provides once it lands, so you can time purchase orders against your actual sales velocity rather than reordering on a fixed calendar schedule.
Worked example
Using the values the calculator loads with:
Inputs
- Average daily sales: 22 units
- Supplier lead time: 35 days
- Safety stock: 150 units
- Typical reorder quantity: 1500 units
Results
- Reorder point: 920
- Expected demand during lead time: 770
- Days of coverage per reorder: 68
What each field means
Inputs
- Average daily sales (units)
- The average daily sales used in the calculation, measured in units. Starts at 22 units so you have a working example on load.
- Supplier lead time (days)
- The supplier lead time used in the calculation, measured in days. Starts at 35 days so you have a working example on load.
- Safety stock (units)
- The safety stock used in the calculation, measured in units. Starts at 150 units so you have a working example on load.
- Typical reorder quantity (units)
- The typical reorder quantity used in the calculation, measured in units. Starts at 1500 units so you have a working example on load.
Results
- Reorder point
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Expected demand during lead time
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Days of coverage per reorder
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How do I calculate safety stock if I don't already have a number?
Use a dedicated safety stock calculation based on demand variability and lead time variability rather than guessing. A common simple approach is to multiply your average daily sales standard deviation by a service-level factor (often 1.65 for ~95% service level) and by the square root of lead time in days.
Should I use average lead time or worst-case lead time?
Average lead time for the reorder point calculation itself, with the variability captured separately in your safety stock buffer. Using worst-case lead time in both places double-counts the risk and leads to excess inventory.
How often should I recalculate reorder points?
Monthly for stable SKUs, and immediately after any change in supplier lead time, a seasonal demand shift, or a meaningful change in sales velocity from a promotion or new sales channel. Stale reorder points are one of the most common causes of preventable stockouts.
What if my sales velocity varies a lot by season?
Calculate reorder points separately for peak and off-peak periods using the seasonal average daily sales for the upcoming lead time window, not a trailing 12-month average that blends high and low seasons together.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Inventory Reorder Point Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/ecommerce-reorder-point
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/ecommerce-reorder-point" target="_blank" rel="noopener">Inventory Reorder Point Calculator — RevenueLab</a> (2026).</p>
Source: [Inventory Reorder Point Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/ecommerce-reorder-point) (2026).