Can I go ahead and buy my min for next month even if my min for this month aren't up?

Hello, Missmjsmith82, we're here to help give you more context on refilling your PREPAID minutes.

As previously mentioned by our ACE, formerlyknownas, you should wait until it's time to refill your minute within 30 days, just to avoid your minutes expiring early. 

We recommend using this resource to refill your PREPAID amount due.

Use our automated phone service

Call 611 from your AT&T Prepaid phone or call 800.901.9878 from another phone.

1. Say Payment at the main menu.
2. Select Make a payment.
3. Choose either debit card, credit card, or refill card. You can’t make a payment with a checking account when calling 611.
4. Follow the prompts to complete your payment. For an AT&T Prepaid card, you'll enter the Prepaid PIN from the back of the card or from the PIN receipt.

Use Star Services

Dial *888* + PIN number + # (for example, *888*1234567899874#). We’ll confirm that your payment (refill) was applied to your account.

Please let us know if this helps. Thanks so much for reaching out to AT&T Community Forums!

Nelson, AT&T Community Specialist. 

I'll assume min =minutes

If you are still on a pay-per-use minute plan, and refill each 30 days, You should not refill early because your refill has a 30 day expiration date.  Refilling early would cause your balance to expire early and service would end before your 30 days is up.

Note the balance expiration schedule in the TOS