If upgrading to a higher plan or downgrading to a lower plan at any time during the month, the monthly charges are calculated based on the # of days in the previous plan and # of days in the new plan adjusted on a daily basis. All charges occur on the day of the month you purchased your initial plan. For this reason, when you upgrade, the charge for the next month is a bit higher from the price of your new plan - it includes a few days at the higher rate embedded in the invoice. The same stands for downgrades, the charge for the next month is a bit less than your new plan as it includes a few days at the lower rate. All these adjustments are shown on the invoice as separate items so you can see what has been applied.
Note that for Unlimited Plans that have soft limits there might be an extra charge based on the number of additional users that accessed your account (over and above the allowance for your plan) during the last 30 days. This is also presented as an additional item on your invoice.
If you cancel your subscription during your monthly cycle, your portal will remain active until the end of the billing period, when it will be canceled and not renewed.
For example, if you signed up initially on the 10th of the month for the Small Plan based on registered users for $39/month you would be charged $39/month on the 10th of each month. If 3 months later you upgraded on the 28th of the month to the Basic Plan for $129/month then the calculation would be as follows:
Month 1: $39
Month 2: $39
Month 3: $39 (You upgrade during this month to Basic plan but we do not charge you directly)
Month 4: $129 + $28.2 transferred difference
Month 5: $129
The transferred difference in our example is calculated as: # remaining days in the previous plan * previous plan price + # of days in the new plan * new plan price = -18/30*$39+12/30*$129 = -$23.4 + $51.6 = $28.2