List the paired values for the two variables as (x_1, x_2, dots, x_n) and (y_1, y_2, dots, y_n)
Compute the mean of each variable: (bar{x} = frac{sum x_i}{n}), (bar{y} = frac{sum y_i}{n})
Subtract each mean from its corresponding values: (x_i – bar{x}), (y_i – bar{y})
Multiply each pair of deviations: ((x_i – bar{x})(y_i – bar{y}))
Sum all the products: (sum (x_i – bar{x})(y_i – bar{y}))
Divide by (n) for population covariance: (text{Cov}(X,Y) = frac{sum (x_i – bar{x})(y_i – bar{y})}{n})
Divide by (n-1) for sample covariance: (text{Cov}(X,Y) = frac{sum (x_i – bar{x})(y_i – bar{y})}{n-1})