How do you analyze time complexity of recursive algorithms?

For recursive algorithms, count the number of recursive calls and the work done per call. If each call makes two recursive calls and does O of one work, the total is O of two to the power of n. Draw the recursion tree: the total work is the sum across all levels. For divide-and-conquer, the Master Theorem provides formulas based on the recurrence relation: if T of n equals a times T of n over b plus O of n to the d, the complexity depends on how log base b of a compares to d.