How to automate invoice processing with AI, step by step

01Why invoices are a good first project

The work is repetitive, the rules are clear and the result is easy to check: every field has exactly one right answer. In June 2026, the Business Development Bank of Canada reported that only 30% of Canadian small and medium businesses use generative AI. If you are not one of them yet, invoices are a safe place to start, because when the AI gets something wrong, you can see it before it costs you anything.

02The workflow in five steps

1. 1
   One door in

   Every invoice lands in one address.

2. 2
   AI extraction

   A model reads the invoice and returns the fields.

3. 3
   Rule checks

   Simple rules check the math and look for duplicates.

4. 4
   Human approval

   A person approves, or answers a question.

5. 5
   Accounting

   The approved bill goes into your accounting software, with the original attached.

03Step 1: one address for all invoices

Create one address just for invoices (for example invoices@ your domain), ask every supplier to use it, and forward anything that lands in a personal inbox. Paper invoices get photographed or scanned and sent to the same place. One door in means nothing gets lost, and your automation only has to watch one inbox.

04Step 2: extraction with a prompt that never guesses

A general AI model can now read an invoice and return the vendor, invoice number, dates, purchase order, every line, the subtotal, GST, QST and total, with no template and no training, as long as you say exactly what you want back. The key line is the last one: if a field is missing or unreadable, write null and ask a question. Never guess. A model that is allowed to say “I don't know” flags the problem instead of inventing a number that looks right.

You are an accounts payable assistant for a small business in Quebec.
From the invoice below, return ONLY a JSON object with these fields:
vendor_name, invoice_number, invoice_date, due_date, po_number, currency,
line_items (description, quantity, unit_price, amount), subtotal, gst, qst, total.

Rules:
- Copy values exactly as printed. Dates as YYYY-MM-DD, amounts as numbers.
- If a field is missing or you can't read it, write null and add a short
  question to a list called "questions".
- Never guess. Never calculate a value that isn't printed.

05Step 3: let rules check the math, not the model

Don't let the model check its own math. Let it read, and let a few plain rules in your spreadsheet or automation tool do the checking:

• Does subtotal + GST + QST equal the total?
• In Quebec, is GST 5% and QST 9.975% of the subtotal?
• Have we already seen this vendor and invoice number?
• Does the purchase order exist?

The duplicate rule earns its keep fast. In our test, the second copy of an invoice arrived three days later with “reminder” in the subject: same vendor, same number, same amount. The rule sent it to a review pile instead of the payment run, with a note explaining why.

06The test that matters: a blurry photo

Our hardest sample was a phone photo, a little blurry, with the invoice number cut off. The model left the number empty and asked a question instead of inventing one. And the math rule caught what the model was told not to judge: the printed total was 1,697.78, but the lines add up to 1,679.78. Two digits swapped. Flagged, not paid.

{
  "vendor_name": "Atelier Nord Fasteners",
  "invoice_number": null,
  "invoice_date": "2026-10-04",
  "po_number": "PO-3390",
  "subtotal": 1461.00,
  "gst": 73.05,
  "qst": 145.73,
  "total": 1697.78,
  "questions": [
    "The top of the page is cut off in the photo and no invoice number is visible. What is the invoice number?"
  ]
}

07Step 4 and 5: approval, then accounting

Everything that passes the checks lands in one approval list with the original PDF one click away. Your bookkeeper, or you, skims and approves, and only then is the bill created in your accounting software. Anything flagged waits with its question attached. The person becomes the checker, not the typist.

08What tools do you need?

Probably fewer than you think. Many accounting tools already include a bill capture inbox, so check yours first. For more control, automation platforms such as Zapier, Make, n8n or Power Automate can run an AI step in the middle of a workflow: watch the inbox, extract, check, then send the result to your approval list. Start with what you already pay for.

09What it's worth

Say invoices take four hours a week at a loaded cost of $35 an hour: about $6,720 a year. With the calculator's typical assumption that around 70% of invoicing can be automated, that frees roughly 134 hours, about $4,700 a year; even the cautious case is around $2,800. Try your own numbers in the free calculator.