Scope

How Proration is calculated when a sub is upgraded/downgraded?

Formula to calculate proration.

Calculate Proration when calendar billing is ON.

Summary 

Proration is calculated in two types: day-based and milli-second based. 

The Formula to calculate proration : (Prorated Term / Regular Term) * Plan Amount (OR) (Plan Amount / Regular Term) * Prorated Term

We have migrated to new Self-Serve Calendar Billing configuration from 23 March 2023. Self-Serve Calendar Billing allows you to add multiple Site-level & Plan-level configurations also supports Yearly billing frequency. With this new configuration, you can manage both SaaS and E-Commerce business. Besides, the Advance trigger allows you to set calendar billing for specific events. Reach out to our support to enable this feature on your site.

Solution 

Use-case:  Calendar billing is set to 1st to every month and prorate immediately. Now I start a sub with 649$ on 31st JAN . Now my renewal will be 1st of FEB. So my first invoice generated will be prorated. the prorated amount for 1 day is accounting to 23.18$

The Formula to calculate proration : (Prorated Term / Regular Term) * Plan Amount (OR) (Plan Amount / Regular Term) * Prorated Term

Now according to the above formula if we calculate the above use case then - 

In this case, the prorated term is Jan 31st to Feb 1st.  Internally, we calculate the per-day amount by converting that to a regular term which is Jan 31st to Feb 28th. The number of days between Jan 31st to Feb 28th is 28 so 649/28 = 23.1785.

The per-day amount is then multiplied by the number of days in the prorated term which is 1 day in this case. So the final amount charged was $23.18.