Calculating Total Amount with Partial Period Proration
This article introduces how to calculate total amount for recurring charges with partial period proration. It gives you the formulas and examples of calculating total amount and prorated amount.
Calculating Total Amount with Partial Month Proration
With recurring charges for any periods less than a month, the total amount is equal to the sum of prorated amount for partial months plus charge amount for full months.
The calculation of prorated amount for partial months depends on the setting of the following billing rules:
 Bill recurring charges for partial month (with monthly based billing periods)?
 When prorating a month, assume 30 days in a month or use actual days?
If Bill recurring charges for partial month (with monthly based billing periods)? is set to Yes, prorated amount is calculated. You can choose to calculate prorated amount either using 30 days in a month or using actual days in a month by setting the When prorating a month, assume 30 days in a month or use actual days? billing rule.
The following table describes formulas and examples of total amount calculation with different billing rules.
When prorating a month, assume 30 days in a month  When prorating a month, use actual days 

Total_amount = Price_per_month * (Number_of_full_months + (Prorated_days/ 30) ) 
Total_amount = Price_per_month * (Number_of_full_months + (Prorated_days/Actual_number_of_days_of_the_prorated_month) ) 
Example Scenario:
 Charge Model: Per Unit Pricing
 List Price: $100 with the list price base option of Month
 Unit: 1
 Billing Period: Month
 Subscription Term Start Date: 01/01/2018
 Subscription Term: 12 months
 Trigger Condition: Upon Contract Effective
 End Date: Align to Subscription End Date
 Billing Day: Specific Day of Month, 15th of the month
 Billing Period Alignment: Align to Charge
 Target Date for the Bill Run: 02/14/2018
Example 1
With the above example scenario and the billing rule of assuming 30 days in a month, the total amount is calculated based on the formula:
 Number of full months: 1 (01/15/2018  02/14/2018)
 Prorated days: 14 days
Total amount on the invoice: $146.67 = $100 * (1 + 14/30)
Example 2
With the above example scenario and the billing rule of using actual days in a month, the total amount is calculated based on the formula:
 Number of full months: 1 (01/15/2018  02/14/2018)
 Days in the prorated month: 14 days
 Actual number of days in the prorated month: 31 days
Total amount on the invoice: $145.16 = $100 * (1 + 14/31)
Calculating Total Amount with Partial Week Proration
With recurring charges for partial weekly billing periods, the total amount is equal to the sum of prorated amount for partial weeks plus charge amount for full weeks.
The calculation of prorated amount for partial weeks depends on the setting of the Bill recurring charges for partial week (with weekly based billing periods)? billing rule. If this billing rule is set to Yes, the prorated amount is calculated.
You can use the following formula to calculate the total amount:
Charge_amount = Price_per_week* (Number_of_full_weeks + (Prorated_days/7 ) )
Example Scenario:
 Charge Model: Per Unit Pricing
 List Price: $100 with the list price base option of Week
 Billing Period: Week
 Subscription Term Start Date: 01/01/2018
 Subscription Term: 5 weeks
 Billing Day: Specific Day of Week, Wednesday
 Billing Period Alignment: Align to Charge
 Target Date for the Bill Run: 01/31/2018
In this example, the total amount is calculated based on the formula:
 Price per week: $100
 Number of full weeks: 5 weeks
 Prorated days: 2 days (01/01/2018  01/02/2018)
Total amount on the invoice: $528.57 = $100 * (5 + 2/7)
Calculating Total Amount with Partial Period (Quarter, Semiannual, or Annual billing Periods)
This feature is in Limited Availability. If you want to have access to the feature, submit a request at Zuora Global Support.
With recurring charges for partial quarter, semiannual, or annual billing periods, the total amount is equal to the sum of the prorated amount for partial billing periods plus charge amount for full billing periods.
The calculation of prorated amount for partial billing periods depends on the setting of the following billing rules:
 Prorate recurring charges for partial period?
 When prorating periods greater than a month, prorate by month first, or by day?
 When prorating a month, assume 30 days in a month or use actual days?
If Prorate recurring charges for partial period? is set to Yes, the prorated amount is calculated. The results of the proration depend on the combination of the When prorating periods greater than a month, prorate by month first, or by day? and When prorating a month, assume 30 days in a month or use actual days? billing rules.
The following table provides you the formulas and examples of the total amount calculation with different bill rules.
When prorating a month, assume 30 days in a month  When prorating a month, use actual days  

When prorating periods greater than a month, prorate by month
(If Bill recurring charges for partial month (with monthly based billing periods)? billing rule is set to Yes) 
Total_amount = Price_per_month * (Number_of_full_months + (Prorated_days/30) ) 
Total_amount = Price_per_month * (Number_of_full_months + (Prorated_days/Actual_number_of_days_of_prorated_month) ) 
When prorating periods greater than a month, prorate by day 
Total_amount = Price_per_billing_period * (Number_of_full_billing_periods + Prorated_days/Number_of_days_of_prorated_period) Use 30 days to calculate Number_of_days_of_prorated_period. For example:

Total_amount = Price_per_billing_period * (Number_of_full_billing_periods + Prorated_days/Actual_number_of_days_of_prorated_period) 
Example Scenario:
 Charge Model: Per Unit Pricing
 List Price: $1200 with the list price base option of Billing Period
 Unit: 1
 Billing Period: Annual
 Subscription Term Start Date: 01/01/2018
 Subscription Term: 12 months
 Trigger Condition: Upon a Specific Date 07/14/2018
 End Date: Align to Subscription End Date
 Billing Day: Subscription Start Day
 Billing Period Alignment: Align to Term Start
 Target Date for the Bill Run: 12/31/2018
Example 1
With the above example scenario and the following billing rules:
 Assuming 30 days in a month
 Prorated by month when prorating periods greater than a month
The total amount is calculated based on the formula:
 Price per month: $1200/12
 Number of full months: 5 months (August, September, October, November, and December)
 Prorated days: 18 days (July 14  July 31)
Total amount on the invoice: $560.00 = $1200/12 * (5 + 18/30)
Example 2
With the above example scenario and the following billing rules:
 Using actual days in a month
 Prorated by month when prorating periods greater than a month
The total amount is calculated based on the formula:
 Price per month: $1200/12
 Number of full months: 5 months (August, September, October, November, and December)
 Prorated days: 18 days (July 14  July 31)
 Actual number of days of the prorated month: 31 days
Total amount on the invoice: $558.06 = $1200/12 * (5 + 18/31)
Example 3
With the above example scenario and the following billing rules:
 Assuming 30 days in a month
 Prorated by day when prorating periods greater than a month
The total amount is calculated based on the formula:
 Price per billing period: $1200
 Number of full billing period: 0 year
 Prorated days: 171 days (July 14  December 31)
 Number of days of the full period: 360 days
Total amount on the invoice: $570.00 = $1200 * (171/360)
The actual prorated amount can only be less than or equal to the total amount of the original invoice.
Example 4
With the above example scenario and the following billing rules:
 Using actual days in a month
 Prorated by day when prorating periods greater than a month
The total amount is calculated based on the formula:
 Price per billing period: $1200
 Number of full billing period: 0 year
 Total number of days of the partial period: 171 days (July 14  December 31)
 Actual number of days of the full period: 365 days
Total amount on the invoice: $562.19 = $1200 * (171/365)
See Billing Period Alignment for more information about charge calculation with different billing period alignments.
When billing period is the subscription term
When the billing period is the subscription term, the system will calculate the proration amount according to the list price. Therefore, if the list price is monthly, the system will calculate the amount monthly; if the list price is weekly, the system will calculate the amount weekly, etc.