The general unwritten but widely followed rule is to tip 15 percent of the total cost spent trekking. If you are trekking solo, the rule of thumb is to tip $5 per day or equivalent for guides and $2 to $4 per day or equivalent for porters.
For group trekking, you can tip $10 per day for guides and $5 per day for porters. You can also tip as you wish based on the weight carried and the service provided.