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Lead Time Demand Calculator

Work out lead time demand instantly with clear inputs, formula shown and shareable results.

About Lead Time Demand Calculator

Lead time demand is what you expect to sell while a replenishment order is in transit. Adding safety stock sized as z times the demand standard deviation times the square root of lead time gives the reorder point that protects your chosen service level.

Formulas

Lead time demand

LTD = Average daily demand x Lead time (days)

Safety stock

SS = z x sigma_daily x sqrt(Lead time)

Reorder point

ROP = LTD + Safety stock

Worked example

With the default values below, Lead Time Demand Calculator returns Reorder point of 1,865. Change any input above and every figure here is recalculated in your browser.

Inputs used

Average daily demand
120
Supplier lead time
14
Daily demand standard deviation
30
Service factor z
1.65

Results

Reorder point
1,865
Lead time demand
1,680
Safety stock
185
Days of cover at the reorder point
15.5

Step by step

  1. 1Values used
  2. 2Lead time demand
  3. 3Safety stock
  4. 4Reorder point
  5. 5Reorder point= 1,865
  6. 6Lead time demand= 1,680
  7. 7Safety stock= 185
  8. 8Days of cover at the reorder point= 15.5

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • This is an estimate for general information and not professional financial, tax or legal advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Which z value matches my service level?

1.28 for 90%, 1.65 for 95%, 2.05 for 98% and 2.33 for 99% cycle service level.

Why the square root of lead time?

Daily demand variations are independent, so variance adds over the lead time and standard deviation grows with the square root of the number of days.

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