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Reorder Point Calculator

Calculates the reorder point and safety stock for your service level, plus the economic order quantity and how long stock on hand will last.

Calculators Nothing uploaded No sign-up Free, unlimited
Calculators tool
Standard deviation of daily units
Leave 0 to skip the order-now check
Leave 0 to use daily demand × 365
Enter your figures and press Calculate.
In short Reorder Point Calculator is a free online tool on inputtesthub.com that calculates the reorder point and safety stock for your service level, plus the economic order quantity and how long stock on hand will last. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Reorder Point Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Reorder Point Calculator

The Reorder Point Calculator calculates the reorder point and safety stock for your service level, plus the economic order quantity and how long stock on hand will last. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Deciding when to place the next purchase order.
  • Sizing a buffer for a supplier whose lead time slips.
  • Finding the order quantity that balances freight against storage.

Details

95% servicez = 1.6449
99% servicez = 2.3263
Safety stockGrows with the square root of lead time
Variable lead timeCosts more buffer than long lead time
EOQWhere ordering cost equals holding cost

The maths behind it

This tool uses reorder point = demand during lead time + safety stock, where safety stock = z × √(lead time × demand variance + demand² × lead time variance), and EOQ = √(2 × annual demand × order cost ÷ holding cost). Every intermediate value is shown on screen, so the result can be checked by hand.

Lead time variability is usually the bigger term and is usually the one left out. A supplier who reliably takes 30 days needs less buffer than one who averages 20 but sometimes takes 40, and any model that only uses average lead time cannot see the difference.

Where this tool stops

It assumes demand is roughly normal and independent day to day, which breaks for seasonal goods, promotions and anything sold in occasional large orders. EOQ additionally assumes steady demand, a fixed order cost and no volume discounts — treat it as a sanity check on order size, not an instruction.

Frequently asked questions

What does a 95% service level actually mean?
A 95% chance of not running out during any one replenishment cycle — not 95% of the year. If you reorder ten times a year, you would still expect a stockout roughly every other year. That is why the last few points of service cost so much: going from 95% to 99.9% nearly doubles the safety stock.
Why does shortening lead time help so much?
Safety stock scales with the square root of lead time, so cutting lead time from 28 days to 14 removes about 29% of the buffer, not half — but it also halves the demand you have to cover during the wait, and that part is linear. Together the reorder point falls sharply, which is why lead time is usually the cheapest thing to attack.
Do I need an account to use the Reorder Point Calculator?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the utility.
Does anything I enter leave my computer?
No. The Reorder Point Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses reorder point = demand during lead time + safety stock, where safety stock = z × √(lead time × demand variance + demand² × lead time variance), and EOQ = √(2 × annual demand × order cost ÷ holding cost). The full working is printed under the result, so you can follow every step rather than trusting a black box.
What problem does the Reorder Point Calculator solve?
In practice it gets used for three things: deciding when to place the next purchase order. Sizing a buffer for a supplier whose lead time slips. Finding the order quantity that balances freight against storage. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What are the limits of the Reorder Point Calculator?
It assumes demand is roughly normal and independent day to day, which breaks for seasonal goods, promotions and anything sold in occasional large orders. EOQ additionally assumes steady demand, a fixed order cost and no volume discounts — treat it as a sanity check on order size, not an instruction. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What are the reference figures here?
95% service is z = 1.6449. 99% service is z = 2.3263. Safety stock is Grows with the square root of lead time. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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