A company is offering a subscription service with a standard monthly price of US$200.

In Salesforce Billing and Subscription Management, proration is applied when a customer begins or ends service mid-period. With Monthly Proration and Calendar-Aligned Boundaries, the system determines the correct prorated charge by calculating the proportion of the month the service is active.

For a start date of March 20, the service is active from March 20 to March 31. The correct proration multiplier formula is:

Number of remaining days in March / Total number of days in March

This calculates the billable fraction of the month and applies it to the monthly price. In March, there are 31 days, so the proration multiplier is:

(31 - 20 + 1) / 31 = 12 / 31 ≈ 0.3871

This aligns with Salesforce's proration logic when "Partial Periods Allowed = Yes" and “Align to Calendar” is selected.

Option B incorrectly calculates used days, not remaining days.

Option C applies to Annual Proration, not monthly, and is not relevant here.

Exact Extracts from Salesforce Revenue Cloud Documents:

Subscription Management Implementation Guide – “Proration Settings”:“For calendar-aligned billing periods, the proration multiplier is calculated as (remaining days in period / total days in period).”

Billing Implementation Guide – “Partial Period Calculation Examples”:“When partial periods are enabled, proration applies from service start to end of period based on remaining days.”