Mental health disorders like depression and anxiety are common and significantly impact wellbeing, yet mental healthcare remains underfunded in low-income countries. Psychotherapy is an effective treatment that can be delivered cheaply by lay counsellors. This in-depth report evaluates the cost-effectiveness of two charities providing such therapy in Africa: Friendship Bench and StrongMinds. We estimate that Friendship Bench has a cost-effectiveness of 49 WELLBYs per $1,000 donated ($21 per WELLBY), and StrongMinds has a cost-effectiveness of 40 WELLBYs per $1,000 ($25 per WELLBY). Our results show that both charities are 5-6 times more cost-effective than cash transfers at improving subjective wellbeing. This is the fourth iteration of our analysis, which includes new data and refined methods. Our results are similar to the last version of the report, and we conclude that these two organisations are the most cost-effective charities (which are also well-evidenced) we have evaluated to date.