Sort the data in ascending order
Find the median of the data set
Split the data into a lower half and an upper half
Q1 is the median of the lower half
Q3 is the median of the upper half
If the data set has an odd number of values, exclude the overall median from both halves
If the data set has an even number of values, split the data into two equal halves
Use the middle value of each half as the quartile
For grouped or frequency data, locate the 25th percentile for Q1 and the 75th percentile for Q3