This is very complex. I am also trying to figure out, and numbers are always confusing here. Did you find the answers?
Topic summary
Focus: How Shopify determines “days remaining” in an app’s billing cycle for proration when merchants upgrade/downgrade.
Scenario & assumption: App installed on 2023-07-01T12:00 UTC with no trial; next billing date shown as 2023-07-31 (fixed 30‑day cycle). Uncertainty arises because Shopify displays a date without a time component.
Key question 1: Does the installation time affect the cycle boundary? Specifically, does the new cycle begin at 2023-07-31T00:00 UTC or at 2023-07-31T12:00 UTC?
Key question 2: How is “days remaining” computed for proration? Example: if a shop downgrades on 2023-07-30T20:00 UTC, is the remaining count 1 day or 0? Does time-of-day change the result (e.g., 2023-07-30T00:30 vs later that day)?
Definition: Proration = proportional charge adjustment based on the unused portion of the billing period.
Status: No authoritative answer provided. Another participant notes the complexity and asks if a resolution was found. Discussion remains open with these calculation rules unresolved.