Hi there, cleanbydanielle. To include GST on your invoices, you must first ensure the Sales Tax feature is active and your rates are configured in QuickBooks Online.
To get your sales tax up and running, click the Gear icon and select Set up tax. Hit the + icon to start, then just fill in your start date, filing frequency, and reporting method. Then click Done to save your changes.
Once the tax feature is active, stay on the same page to set up the specific rate. Select Create another rate for existing sales tax and choose GST/HST. Enter the 5% GST details and hit Save to finish.
To apply GST to a specific invoice, go to + icon > Invoice. Ensure the tax setting is set to Inclusive of tax. Under the Tax Code column for your items, apply the GST rate you just created. Once the line items are added, you can either Save the document or select Review and send to forward the invoice to your customer.
Please refer to this article for more information on setting up your taxes: Set up and use sales tax in QuickBooks Online.
If you have additional questions, feel free to comment below.
