Enter the annual demand and the optimal order size into the Time Between Orders Calculator. The calculator will evaluate the Time Between Orders. 

Time Between Orders Formula

The following two example problems outline the steps and information needed to calculate the Time Between Orders.

TBO = WD / (D/Q)


  • TBO is the Time Between Orders (working days)
  • WD is the working days per year
  • D is the annual demand 
  • Q is the optimal order size 

To calculate the time between orders, divide the working days per year by the result of the annual demand divided by the optimal order size.

How to Calculate Time Between Orders?

The following steps outline how to calculate the Time Between Orders.

  1. First, determine the annual demand. 
  2. Next, determine the optimal order size. 
  3. Next, gather the formula from above = TBO = 250 / (D/Q).
  4. Finally, calculate the Time Between Orders.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

annual demand = 500

optimal order size = 20

TBO = 250 / (D/Q) = ?