The computation of Yaka! is impacted by three things; the discounted Units, the Service Fee, and the VAT. Discounted Units (15 units each at Shs 150/=) are earned once in 30 days. Service Fee of Shs 3360/= is charged once in 30 days. VAT is charged on every transaction. Therefore if one makes multiple transactions during 30 days, he earns discounted units once, and service fee is levied once. These affect the units you get in each transaction.