# Consultant invoicing: day rates, milestones and retainers

> Identify advisory work by period, purchase reference and milestone. Invoice consulting projects and automate fixed monthly retainers.

URL: https://factuurmaken.nl/en/voor-wie/consultant
Last updated: 2026-09-27

Your client needs to connect each invoice to a project and period. You need to bill advisory work without reconstructing every agreement at month-end.

## Help the finance team recognise the assignment

The person receiving your advice may not process the invoice. Ask for the legal customer name, billing address and purchase reference at the start. Include that reference, the project and the service period in your description.

“Warehouse process analysis — September advisory days, order INK-104” explains more than “September advice”.

## Example: advisory work alongside a retainer

| Invoice line                        | Quantity      | Scope                               |
| ----------------------------------- | ------------- | ----------------------------------- |
| September process advisory retainer | 1 month       | Availability and meetings as agreed |
| Implementation team workshop        | 2 days        | Agreed outside the retainer         |
| Phase 2 evaluation report           | 1 deliverable | Separate project milestone          |

Use your quote to define the phases included in a fixed project fee. For day-rate work, keep your own record of the days worked.

## Automate the fixed part

Create a recurring schedule for a retainer with an unchanged monthly amount. Invoices can be created and sent automatically at the chosen interval. You need a subscription that includes recurring invoices even if you only have a few clients.

### Are additional advisory days automatically added?

No. A schedule knows the agreed lines, not your actual working days. Invoice extra work separately or review and update a draft before sending. This keeps the retainer and additional charges clear.

## A good fit if

- You invoice advisory days, project phases or fixed retainers
- Your clients ask for project or purchase references
- You want to automate fixed monthly fees

## Not the right choice if

- You need project budgets, margins and timesheets in one consulting system
- You require an integration with a mandatory procurement portal