sales trend and forecasting

I work in sales, i'm a sale coach. I'm trying to create an excel sheet where i can calculate monthly sales trend.

For example:

JOHN Quota is 30 ( he has to bring 30 new customers a month)

In the last report August 8th John has sub scripted 11 customers. In other words around 36% of his goal within the first week. I want to know much % is he trending if he continues doing what he is doing.

Can anyone point me to where i can find this kind of sheet, or how would i go about calculating this to input into excel,

thank you