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Every invoice gets a number automatically. You can override it with your own, as long as it is unique in the workspace.

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The automatic number

The automatic format is INV- followed by a zero-padded sequence. The padding is a minimum of six digits. Past 999,999 the number grows – nothing is truncated.

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The sequence is gapless

Numbers are allocated one after another with no gaps and no reuse.
The last row is the one that surprises people. Even when you type your own number, the internal sequence moves on. That keeps the ordering and the audit trail intact, so invoices always sort in the order they were raised.

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Custom invoice numbers

Type your own in the Invoice number field on the builder. The field’s placeholder shows the next automatic number, for example Auto: INV-000042. The helper text reads “Leave blank to use the next automatic number. A custom number must be unique within this workspace.”

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Uniqueness is checked as you type

TimeTracker checks availability while you type. If the number is taken you see an inline error under the field:
That invoice number is already used by another invoice. Choose a different one.
The Save draft and Send invoice buttons stay disabled until you fix it. Editing a draft and re-saving it with the number it already has is never treated as a clash.

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How to set a custom number

1

Open the builder

Invoices → Create invoice, or Edit on a draft.
2

Find the Invoice number field

It sits below the client, project and type row.
3

Type your number

The availability check runs as you type.
4

Save

The number you typed is what the client sees, in the app, in the PDF and in every email.
To go back to automatic numbering on a draft, clear the field and save.

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Where the number appears

Everything shows the same number, so a client quoting “invoice 2026/BLUEBIRD/001” always matches what you see.

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Example

Northwind Studio switches to their accountant’s format mid-year. Behind them the sequence still ran 1, 2, 3, 4, so the invoices stay in the order they were raised.

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Permissions

See /invoicing/invoice-permissions.

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Common questions

Not on the automatic number. If you need a different prefix, type it as a custom number on each invoice.
Not for the automatic sequence – it runs for the life of the workspace. Use custom numbers such as 2026/001 to restart yourself.
Because an invoice was raised in between, possibly with a custom number, possibly one that was later voided. The sequence never goes backwards.
Not the automatic one – it is gone for good. A custom number is also still taken by the voided invoice, so pick a new one.
No. Editing rebuilds the invoice in place and keeps its number.
Yes. Numbers are unique within a workspace, not across them.

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Troubleshooting

Create an invoice

Where the number field lives.

Edit a draft invoice

Why the number never changes.

Void an invoice

Why a voided number is not reused.

Download an invoice PDF

The number in the filename.

Invoicing overview

The whole flow.

Invoice permissions

Who can set a number.