If you add an additional user to the subscription plan in the middle of month, then our system would automatically issue an invoice with a prorated price for the additional user for the remaining part of the month.
MRR would only be increased for the remaining part of the month, not the full month. You can see what dates the additional user would contribute to by looking at the start and end dates next to the line item charge in the invoice.
For example, let's say adding an additional user costs $10, but since you're adding them halfway through the month of June, the customer is charged $5 for the remainder of the month.
If you look at the invoice, the start and end date next to that line item would show June 15-June 30. These are the dates that the additional user would contribute to MRR. So, the $5 charge from the additional user would be applied from June 15-June 30.
$5 divided by 15 days = $0.33 per day contribution to the MRR calculation during those dates.