Tipping is never an easy subject to broach, but is commonly expected in most parts of Africa as it makes up an important part of guides and porter's salaries.
#1. Please remember that tips are always discretionary. Guidelines are provided for guidance only.
#2. Tip in proportion to your appreciation of the service you have received and in accordance with what you can afford.
#3. Typically expect to tip between 8-12% of what you paid up front for a trek (to be divided between the team. Budget around $100 - $150 (depending on the length of trek) per person to be distributed amongst the entire trek crew.
#4. It can be difficult judging how much to tip each team member, so most people pool their tip together as a group and present the tip to the chief guide at the gate when leaving the national park. The guide will then divide between the team. This method is preferred as it allows the guide to reward those who have worked hardest behind the scenes (not just what you as clients have seen), If you prefer to tip individually, then expect to tip the cook twice what you'd tip the porter and the guide 1.5x to 2x what you'd tip your cook.