How should I invoice a monthly retainer?

One invoice per period, same client, next sequential number. Description: “September advisory retainer” — not “as discussed.”

Do I need time tracking software to invoice hourly?

You need lines with dates and a rate. A lump “40 hours” with no period is how they ask for a timesheet you do not want in two tools.

Will a portal collect late retainers?

No. Chase with the same share link: day after due, day 3, day 7. A login is not a collection strategy.

Invoicing as a consultant

Consulting invoices stall in AP, not in Slack. Name the company correctly, put the PO on the page, and bill the retainer as a real invoice.

justIssued Team

justIssued10 September 2026Updated 11 September 20261 min read

A consultant billing a company is doing B2B invoicing with a fancier job title. The document still has to survive accounts payable.

Retainer vs project

Monthly retainer: one invoice per period, same client, next sequential number. Description: “September advisory retainer” — not “as discussed.”
Project: estimate first, then invoices on milestones you wrote down. Do not send INV-1 for a number they never accepted. Estimate vs invoice.
Hourly: lines with dates and a rate. A lump “40 hours” with no period is how they ask for a timesheet you do not want to keep in two tools.

What AP needs

Legal name, PO, AP email, Net terms they agreed, tax if you collect it, a unique number. Canadian GST/HST on the GST/HST guide.

Send a share link or PDF to AP, not a screenshot in the hiring manager’s DMs.

When they are late

You already know the schedule: day after due, day 3, day 7. Chase overdue invoices. A portal login is not a collection strategy.

justIssued

Save the company once. Number every retainer. Outstanding is the list. Free is three clients — enough to see if the loop fits before Paid. Start free.

Frequently asked questions

How should I invoice a monthly retainer?: One invoice per period, same client, next sequential number. Description: “September advisory retainer” — not “as discussed.”
Do I need time tracking software to invoice hourly?: You need lines with dates and a rate. A lump “40 hours” with no period is how they ask for a timesheet you do not want in two tools.
Will a portal collect late retainers?: No. Chase with the same share link: day after due, day 3, day 7. A login is not a collection strategy.

Need invoicing in one place?

Save clients, share a public invoice link, and see what remains outstanding. Free covers up to three clients. Paid is $12/month after a 7-day trial.

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