Sum all values in datalist control

Good day friends!
I taught this would be possible but I spend over 2hrs trying to figure this out but to no avail.
This is what I want;
I have datalist control that displays payment details and everything is working fine except one. Which is
I want to display sum of all the payments made on a label control called Aggregate.
For example
Customer Name Amount Date
Paul $2000 20-09-2016
Catherine $5000 20-09-2016
Otes $3000 20-09-2016

Aggregate = Sum of all payments made

Any solution please...
Thanks in advance...