> ## Documentation Index > Fetch the complete documentation index at: https://docs.denari.com/llms.txt > Use this file to discover all available pages before exploring further. # Billing > How work becomes an invoice, and why the billing calendar is separate from the work calendar. Billing picks up where the work leaves off. **Only admins can take billing actions.** ## The one idea **A billing group gets one invoice per billing period.** Not one per project, not one per service. Everything that group owes for that stretch of time is gathered onto one document, split into sections. If a client has monthly bookkeeping, is paying off an audit in installments, and had some advisory work this month, that is one invoice with three sections. ## What happens, in five steps Time is logged against projects as it happens. See [Time](/flows/time). Subscriptions, payment plans, and retainers make their own scheduled charges. See [Pricing](/flows/pricing). At the end of the billing period, everything owed is gathered into one draft invoice per billing group. See [Drafts & review](/flows/drafts-and-review). Once issued, the invoice is locked. See [Issuing & sending](/flows/issuing-and-sending). Payments are applied to invoices and the balance updates itself. See [Payments](/flows/payments). ## Two rules worth knowing up front * **Nothing about money is ever deleted.** Refunds, reversals, corrections, and credit notes all show up as new entries that point back at what they undo. * **Issued invoices don't change.** Once issued, an invoice has a permanent number and a frozen copy. Corrections happen through a credit note, not by editing it. ## The two clocks **One clock decides when the work happens. A separate clock decides when you bill for it.** They usually line up, and they're allowed to differ. | | Work clock | Billing clock | | - | - | - | | **The question** | When is the project made, and when is it due? | When is the work billed, and where does a bill cut off? | | **Set where** | On the engagement's services | On the billing group | | **Set by** | Whoever sets up the engagement | Whoever runs billing | | **Example** | *Make it when the month starts, due 25 days after it ends* | *Invoice quarterly, bill through the 27th* | Both clocks count from the same shared [periods](/flows/periods). They just use them for different jobs. September's work is all of September. If you also bill at the end of the month, the two clocks match and it's one clean September bill. But say you bill on the 27th: work done on the 28th through the 30th is still September work, it just waits for the next bill. Or say you do bookkeeping monthly but invoice quarterly: each month is still its own project, and the quarterly invoice gathers all three, with a line for each. Keeping the clocks apart means you can do the work on the calendar and bill on your own schedule, and changing your billing day never disturbs the work plan. ## The billing pages Who gets the invoice, and how often. How a service is billed, and changing a price. What happens when, and how the cutoff works. Reviewing a draft before it goes out. The point of no return. How money lands and how balances settle. Fixing an invoice you already issued. Unbilled work, budgets, and pre-billing. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.