This article explains where a prorated amount on an invoice comes from. For how to turn proration on or change its settings, see Set and manage invoice proration.
What triggers proration?
Proration only happens when a subscription is amended. For example, an upgrade or downgrade, adding or removing seats or line items, or a cancellation that ends a service period early. Each of these changes gives the affected line item a new start or end date, and Turnstile scales the charge to match the shorter, "effective" period instead of the full billing period.
Editing an invoice directly does not trigger proration. A manual edit to a line item is applied as a direct override, not run through proration math.
How proration is applied to different pricing types
Flat fee and License pricing: Prorated according to your quote, subscription, or plan's proration setting when a service period is cut short by an amendment.
Committed usage pricing: The committed amount is prorated the same way as a flat fee. Usage above the commitment is not prorated; your customer is billed for what was actually used.
Usage pricing (metered, no commitment): Never prorated. Customers are billed for the actual usage recorded in the period, whatever its length.
Percentage pricing: Works like committed usage. A minimum, if set, is prorated; the percentage-based charge itself is never prorated.
One-time charges: Not scaled by proration. If the change removes the period the charge was scheduled in, the charge does not appear on the invoice; otherwise it is charged in full.
How the proration setting affects the amount
Proration is set at the quote, subscription, or plan level, and Turnstile supports three proration settings:
No proration: Full price charged for each service period. Starting mid-month or cancelling early does not reduce the charge.
Day proration: Customers are only billed for the actual days they used a product or service, not the full billing period.
Daily rate = period price ÷ total days in period
Charge = daily rate × active days
Month proration: Any partial month counts as a full month. Example: a 45-day contract is billed as two full months.
See Set and manage invoice proration for where to configure each.
How the adjustment appears on your invoice
When an amendment changes what is owed partway through a period, the original charge stays exactly as it was invoiced. The adjustment shows up as a new, separate line item, dated to the day the amendment takes effect; negative if the change reduced what's owed, positive if it increased it. If there is already an invoice scheduled to be issued the day the amendment takes effect, the adjustment is added as a line on that invoice. Otherwise, it becomes its own invoice, with a total that matches the adjustment.