Can I pay my Zakat monthly? 

Once Zakat becomes due (on your Zakat anniversary) then the scholars are of the opinion that it must be paid without delaying it unless there is a valid reason to do so.

However, if one is unable to pay the Zakat in one payment then he/she may be able to pay in instalments as long as the total amount due is paid.

What about paying monthly before my Zakat anniversary?

Scholars are of the view that Zakat may be paid monthly, as long it is done before the due date. When your due date arrives, you will still need to calculate whether you have paid the right amount. 

Managing monthly payments / keeping money aside for Zakat:

You can estimate how much Zakat you will be expected to pay and ensure you save throughout the year. Scholars accept that this is possible. You should always keep in mind when either paying in monthly instalments or keeping money aside for Zakat, the intention that it is for your Zakat. As mentioned before, When your due date arrives, you will still need to calculate whether you have paid the right amount.