Billing operations
Proration Explained: What Happens When a Subscription Changes Mid-Month
By the Orvlin team · · 3 min read
The question behind the word
A customer upgrades on the 16th. They already paid for the old plan, so charging the full new subscription immediately feels wrong. Proration is the adjustment that accounts for the unused part of the old service and the remaining part of the new one. It is a calculation, not a promise that cash moves today.
For a simple time-based policy, the adjustment is the price difference multiplied by the fraction of the billing period remaining. Your system may use days or precise timestamps. Document that choice before publishing examples, because calendar months have different lengths.
A worked example with two invoice lines
Suppose an illustrative subscription costs $60 for a 30-day period. Exactly 15 days remain when the customer changes to a $100 plan. The unused old-plan credit is $60 × 15/30 = $30. The new-plan charge is $100 × 15/30 = $50. The net adjustment is $20, before taxes, discounts or other charges.
These are teaching figures, not Orvlin prices. A downgrade under the same assumptions reverses the direction: moving from $100 to $60 produces a $20 credit. Whether that credit reduces a future invoice or becomes a refund is a separate policy decision.
An adjustment is not the same as a payment
Stripe documents an important distinction: negative prorations are not automatically refunded, and positive prorations are not necessarily billed immediately. A platform can record an adjustment now and collect it with a later invoice, or generate an invoice when the change takes effect.
Tell the customer both what access changes and when money will be collected. “Your plan is upgraded” does not explain whether a charge is due today. Preview the invoice using the same effective time as the actual change so an estimate does not quietly drift.
Do not turn metered usage into a time credit
Time-based proration fits a fixed access charge. Consumption already delivered usually needs its own measurement and pricing rules. If the customer used 10,000 requests before upgrading, dividing those requests by remaining days is not a meaningful adjustment.
For a hybrid plan, separate the fixed platform charge, included allowance and measured overage. State whether an allowance resets, stays unchanged or changes proportionally. Test an unpaid prior invoice too: crediting unused service that was never paid for can produce an unintended balance.
Before shipping the change
Run upgrades, downgrades, an end-of-period change and a failed-payment case through invoice preview. Check rounding, discounts, tax treatment, credit handling and access activation separately. Save the old and new prices with the effective timestamp.
Then read the customer message aloud. It should explain the remaining-period credit, new charge, net amount and next renewal date without asking the reader to reverse-engineer an invoice.
Frequently asked questions
- Does proration always trigger an immediate charge?
- No. Calculation, invoice creation and payment collection are separate behaviors. Check the settings and explain collection timing.
- Does a downgrade always produce a cash refund?
- No. A credit can remain on the account or offset a later invoice. Refund treatment depends on the agreement and configured policy.