How to set up a project numbering system

To set up a project numbering system, choose a format with a year and a running sequence, such as 2026-042, keep a one-line register of every number issued, and never reuse or change one. Put the number first in every board, folder, file and email subject that belongs to the project.

What makes a good project number?

A good project number identifies one job forever and is short enough to say on the phone. Those two demands rule out most clever schemes.

Which project numbering format should you use?

Most small firms should use the year and a three-digit sequence. Choose something more complicated only when you can name the problem it solves.

Allow for growth when you pick the width. Three digits give you 999 projects a year, and four look silly on a firm that opens 30.

When should a project get its number?

A project should get its number when the work is won, not when you first quote it. If you number every enquiry, your sequence fills up with work you never did, and 2026-042 stops telling you much.

If you need to refer to proposals as well, give them a separate series, such as P-2026-118, and record the project number beside it when it converts. Both numbers then stay honest: one counts proposals and the other counts jobs.

How do you handle phases, variations and sub-projects?

Handle phases and variations with a suffix on the original number, so the base number never changes and all the related work sorts together.

The test for a new number is whether you'd want to see its costs and invoices apart from the first job. If not, it's a suffix or simply another card on the same board.

What does a project register look like?

A project register is a single list holding one row per number issued, and it's the only part of the system that stops two people taking the same number. Here's an invented example.

Give one person the job of issuing numbers, or keep the sheet shared and take the next free row. A cancelled job stays on the list, as 2026-043 does here.

If you're moving from an older scheme, don't renumber past jobs. Start the new series today, and where a new job follows on from an old one, note the old reference, as in the last row. Old files stay searchable under their old numbers.

Should project numbers and invoice numbers be linked?

Project numbers and invoice numbers should be kept separate, with the project number shown on the invoice as a reference. An invoice number has a legal job: under Article 226 of the VAT Directive, it must be sequential, based on one or more series, and must identify the invoice uniquely. A project number has none of those duties.

The Directive allows more than one series, but a separate invoice series per project leaves you with hundreds of them to explain, and any one with a gap invites a question. Keep one invoice sequence and read the guide to numbering invoices for how to set it up.

Then put the project reference on the invoice, in the line description or the notes:

Rear extension, stage 2 of 4, your project reference 2026-042.

Where should the project number appear?

The project number should appear first wherever someone might later search for the job. Here are the usual places.

• Folders: 2026-042 Rear extension. The number first makes the folders sort by date opened.
• File names: 2026-042 Structural calcs rev B.pdf. Avoid / and \, which are path separators.
• Email subjects: [2026-042] Drawing revision B, so a search finds the whole thread.
• Quotes and invoices: as a reference on the document.
• Time records and supplier orders: so costs can be tied to the job. See tracking billable hours by project.

Two spreadsheet traps can break a good format. Short forms such as 26-04 or 2026-04 can turn into dates when typed or opened in Excel, which a three-digit sequence avoids. Plain numbers with leading zeros, such as 00042, lose their zeros in the same way, so keep a letter or a hyphen in the number. Test your format by typing it into a blank sheet and opening a CSV of it before you commit.

Numbering projects in ERPFlow

ERPFlow's projects are boards with names, and they have no automatic project number or next-number counter. Type the number at the start of the board's name, as in 2026-042 Rear extension, and keep the register elsewhere. The guide to how projects work covers boards and cards.

• Finding a job: the board list's search matches the board's name and the linked customer's name or company, and the Name column sorts. Fixed-width numbers put the boards in order.
• Documents: invoices, quotes and orders number themselves in their own sequences, such as INV-2026-0042. The prefix is set in Settings > Business Info. These can't be set per project, which is what you want.
• Linking a project: a quote, order or invoice can link to a board under Linked documents. That link is internal and doesn't print.
• Showing the number to the client: type it in the invoice's line description or Notes, both of which print. The Order number field also prints, but it goes out as the purchase-order reference in the e-invoice, so save it for the client's own PO if they have one.
• Renaming boards: the CSV import of project cards refers to a board by its name, and the board has to exist already. Numbering boards before you import saves redoing the file.

ERPFlow's projects don't carry budgets or per-project costs, so the number helps you find a job, and it won't produce a job cost report.