It depends on the plan that you are on.

For customers who are on our newest SIM card plans (4 GB, 25 GB - both Data Only and Voice+Data SIM):

There will be no data carry-over.

For customers who are on our old SIM card plans (3 GB, 5 GB, 7 GB, 20 GB - both Data Only and Voice+Data SIM):

The data will carry over to the following month (one month only). For example, if you order a 5GB plan and only use 2GB in March, you will have 5GB + 2GB=7GB Data allowance in April.

For Pocket WiFi plans: 

There will be no data carry-over.