How to Invoice as a Consultant (Retainers, Hourly & Project Billing)

As a consultant, your invoice is part of your brand. It is the last thing a client sees after a great engagement, and it sets the tone for whether you get paid in five days or fifty. Done well, invoicing reinforces that you are a professional worth the rate.

Here is how to invoice consulting clients across the three ways consultants typically bill - hourly, by project, and on retainer.

The three consulting billing models

Hourly. You track time and bill it. Best when scope is uncertain. Your invoice should show dates, hours, a short description per entry, and your rate. Transparency here prevents "why was this so much?" emails.

Project / fixed fee. You quote a flat amount for a defined deliverable. Bill in milestones - e.g., 50% to start, 50% on delivery - so you are not financing the whole project yourself.

Retainer. The client pays a fixed amount each month for ongoing access or a block of hours. This is the holy grail for consultants because it is predictable, recurring revenue. Set up a recurring invoice that sends automatically every month so you never have to think about it.

What every consulting invoice needs

Your business name, contact info, and (if applicable) tax/EIN details.

Client and billing contact - route it to the right person or AP team.

Itemized work - for hourly, list entries with dates and hours; for project, list the milestone; for retainer, reference the period ("Strategy retainer - May 2026").

Clear total and due date.

Payment terms and methods - and ideally a "Pay now" link for card or bank transfer.

Payment terms that protect you

New consultants accept whatever terms the client offers. Do not. Net 15 is a healthy default for smaller clients. Larger companies will push for Net 30 or Net 45 - negotiate, and consider a small discount for early payment or a deposit for new clients. For project work, always bill a deposit upfront; it filters out clients who were never serious.

Retainers: set it and forget it

If you have retainer clients, recurring invoices are non-negotiable. The invoice generates on the first of the month, the client pays online, and your revenue arrives without a single manual step. This is also how you turn one-off projects into stable monthly income - propose a retainer at the end of a successful project.

Get paid faster with online payments

Consulting invoices are often larger, and large invoices sit longer when the only option is a bank transfer the client has to set up manually. Add card and ACH payment directly on the invoice, plus automatic reminders, and you remove every excuse for late payment. Many consultants see average days-to-payment drop dramatically just by adding a pay button.

Consultant-specific tips

Track time as you go. Reconstructing hours at month-end loses billable time. Log it live.

Attach the deliverable or summary. A short note of what was accomplished justifies the invoice and reduces questions.

Send promptly. Invoice at the milestone or month-end immediately - the longer you wait, the longer you get paid.

Keep it branded and clean. Remove generic template branding; your invoice should look like your business.

Make it effortless

You bill knowledge, not paperwork hours. Create branded consulting invoices in under a minute, run automatic monthly retainers, track billable time, and accept online payments with reminders. Create your free account - no card required - or try the free invoice generator first. When retainers and online payments become part of your practice, Pro is $19/month.

How to Invoice as a Consultant (Retainers, Hourly & Project Billing)