n8n Google Calendar to Invoice Automation (Docs, Gmail, Sheets)

Turn monthly Google Calendar time into ready-to-send client invoices—automatically

This n8n workflow automatically converts tagged Google Calendar events from the previous month into draft invoices, emails them to you for approval via Gmail, generates a Google Docs PDF invoice, emails it to your client, and logs everything in Google Sheets—so you never double-bill or manually reconcile timesheets again.

What this workflow does

• Runs monthly at 07:00 on the 1st and sets the billing period to the previous calendar month.
• Loads billing data from Google Sheets: client details, tags, hourly rates, currency, and tax rate %, plus invoice/billing logs to prevent duplicates.
• Fetches last month’s events from Google Calendar and parses event titles to find client tags in square brackets.
• Filters events: skips cancelled, all-day, declined, and already-billed events.
• Calculates invoice totals: rounds billable time to your defined increment, applies hourly rates, and calculates totals including tax using the rates stored in Google Sheets.
• Creates draft invoices and sends each draft to you via Gmail for approval (waits for approval or rejection).
• Generates and sends final invoices: for approved drafts, copies a Google Docs invoice template in Google Drive, fills placeholders, exports to PDF, then emails the PDF to the client via Gmail.
• Logs outcomes by appending sent invoice details to an Invoices sheet and writing each billed event to a Billing log sheet.

Use cases

• Freelancers billing clients by hours tracked in Google Calendar.
• Agencies that need monthly invoices with tax based on client-specific rates.
• SaaS operators using n8n to streamline invoice processing without building a full billing system.

Technical details

• Schedule: 07:00 on the 1st of every month
• Integrations/nodes: if, code, no op, Gmail, Google Docs, Google Calendar, Google Sheets, Google Drive (template copy + PDF export)
• Required setup: a Google Sheets file with a Clients tab (Tag, Client, Email, Hourly rate, Currency, Tax rate %) plus sheets for invoice and billing logging.