Pro rata annual subcription billing

Pro rata annual subcription billing

Say a customer buys 10 annual user subscriptions for our Saas product on the 1st July 2017.
So the recurring invoice date would be 1st July 2018.
After 3 months they buy another 10 annual users subscriptions. 
Will Zoho automatically pro rate the new purchases to charge for 9 months (i.e. 9/12ths of the annual subscription) and then bill for 20 users at the renewal date?
If not, how do you suggest managing the scenario?