Unused retainer hours can become additional capacity in the next month or a monetary reduction in the next bill. These are different promises. Choose the agreed rule before creating the next invoice; granting both for the same unused hours can compensate the client twice.
This example is for consultants and small service agencies who sell a defined monthly allowance. It is an operational calculation, not legal, tax or revenue-recognition advice. Contract terms and accounting treatment require their own review.
Compare two explicit agreements
Assume a EUR 2,000 monthly retainer includes 20 hours, and September usage is 14 hours. Six hours are unused. For the credit example only, assume the agreement values an unused hour at EUR 100. A flat retainer does not inherently establish that hourly credit rate.
| Agreed rule | October invoice before tax | October available hours |
|---|---|---|
| Carry all six hours forward | EUR 2,000 | 20 + 6 = 26 |
| Credit six hours at EUR 100 | EUR 2,000 − EUR 600 = EUR 1,400 | 20 |
| No carryforward or credit | EUR 2,000 | 20 |
The third row is a possible explicit agreement, not a default legal entitlement. Under the first rule, your future delivery commitment increases. Under the second, the next amount payable falls. Neither result should be silently inferred from “monthly support.”
Follow the hours into the second month
Suppose October usage is 23 hours. With carryforward, consume the six older hours first, then 17 of the current allowance. Three current hours remain. Whether those three can roll into November depends on the agreed cap and expiry.
With invoice credit, October has only 20 included hours. The additional three need approval under the agreed overage rule. A September credit does not also create six October hours.
Keep a separate capacity ledger: client, cycle, opening carryforward, new allowance, usage, expired hours, closing hours and approval reference. Keep money adjustments in a billing ledger linked to the relevant invoice or credit note. Do not subtract a EUR amount from an hours balance.
Resolve the policy before the next bill
Confirm the maximum carryforward, expiry date, oldest-first consumption, overage approval and what happens at termination. If a client used fewer hours because you could not supply the agreed work, investigate that exception separately; do not treat it as an ordinary unused-capacity calculation.
Send a short cycle summary for confirmation: “September: 20 included, 14 used, six unused. Under our agreed [rule], October is [26 hours at EUR 2,000 / 20 hours at EUR 1,400]. Please confirm before the invoice is issued.” These figures are illustrative and exclude tax.
Map the decision to PayRequest billing
PayRequest's invoice documentation supports custom line items and credit notes that can link to an original invoice. Saving can send a customer notification, so review the intended amount and document type before saving. A credit note is not itself proof of a cash refund.
Keep time tracking and rollover calculations in your own agreed ledger. This workflow does not claim that PayRequest automatically measures consultant hours, rolls capacity forward or nets a credit against the next payment.
Use the retainer product page to align the offer with a clear capacity rule, then review invoicing for the agreed billing document. If an invoice has already been issued, ask your accountant which correction document is appropriate instead of quietly rewriting history.
Editorial note: prepared with AI assistance against documentation checked on 2 October 2026. The arithmetic is an original worked example; no customer outcome or live retainer test is claimed.
