The Chelsea manager was responding to comments from his City counterpart, in which he intimated that the Stamford Bridge outfit had spent the most money in the Premier League over the 10 years.
Mourinho took exception to Pellegrini's interpretation, however, and insists Chelsea spent wisely in the January transfer window in order to comply with UEFA's Financial Fair Play ruling.
"Academically he is an engineer and he does not need a calculator to work it out," the Portuguese said. "(Juan) Mata was sold for £37 million, (Kevin) De Bruyne £18m.
"That is £55m. We brought in (Nemanja) Matic for £21m and (Mohamed) Salah for £11m - that is £32m.
"So £55m minus £32m is £23m. So for Chelsea in this window it is £23m - he does not need a calculator for this.
"They (City) have a team for now, not for 10 years, but for three or four - so experience, potential, power - and not worried about Financial Fair Play because in the summer they spent. You do not need a calculator for this."
Chelsea moved to the top of the Premier League with a 3-0 victory over Newcastle United on Saturday, but Mourinho insists he will not be downbeat if his team fail to win the title.
"It won't be disappointing if we don't finish top," he added. "I will be disappointed if my team can't keep this level (of performance).
"If we don't win tomorrow (at West Brom) it's not just about the title contenders (going above us), it's about Spurs and Everton closing the gap.
"I don't how many points it will take to finish top. Every team in the league will be very influential."
Chelsea continue their assault on the title against West Brom at The Hawthorns on Tuesday, and will be boosted by the return of striker Fernando Torres from a three-week lay-off with a knee injury.
However, captain John Terry will once more miss out with a muscle problem.
"John Terry is still out. Fernando is back and available for selection. I expect John to be back for the next game (against City in the FA Cup)," Mourinho said.
