How to create an invoice | Simple Books Guides

Introduction

An invoice is a document asking a customer to pay for products or services you have supplied. It records the amount the customer owes your business, but it is not proof that you have received the money. The invoice remains unpaid until the payment reaches you and you update its status.

This guide explains how to create an invoice for a customer in Simple Books, from gathering the details to saving, downloading and sending it. It is practical guidance for UK freelancers, sole traders and small businesses, not legal, tax or accounting advice.

Before you create an invoice

Have the following information ready:

Your business name, contact details and address.
Your customer’s correct name, email address and billing address.
A clear description of each product or service and its price before VAT.
The agreed payment terms, such as 14 days.
Your bank account name, sort code and account number if the customer will pay by bank transfer.
Your VAT number and the correct VAT rate if your business is VAT-registered and the sale is taxable.

Simple Books loads your business details, default payment terms and bank details from Account. Complete those details first if necessary; see how to set up your business details.

It helps to agree the price and payment terms with the customer before doing the work. Check which details your invoice must contain for your business type and circumstances.

Create a new invoice in Simple Books

Open the invoice tool and find Create invoice.
Expand Your Business to review the business name, email, website and VAT number loaded from Account. Changes here affect this invoice preview; update Account if the saved business information itself is wrong.
Work down through Client details and Invoice details.

The Invoice preview stays beside the form. It initially asks you to fill in the form; the finished customer-facing version appears when you select Generate Invoice.

Choose or enter the customer

If the customer already has a record, choose them from Saved Customer. Simple Books fills in their Client Name, Client Email, Client Address and saved Payment Terms.

For a new customer, enter those details yourself. Select Save Customer if you want to keep or update the customer record for later invoices. A client name is required to save a customer record, although the invoice form itself does not stop you generating an invoice with a blank customer name. Check it before saving.

Use the customer’s legal or trading name and an address they recognise. The email address is also used when Simple Books prepares an email draft.

Check the invoice number and date

Invoice Number identifies the invoice. Simple Books suggests the next number in the sequence INV-001, INV-002 and so on, based on the highest saved number with that format. You can edit the field, but each saved invoice number must be unique. If the number already exists, including with different capitalisation, Simple Books asks you to use another one.

Invoice Date defaults to today and can be changed. It is normally the date the invoice is issued. Choose the correct date before generating the invoice because it also affects the calculated due date and the period in which the invoice appears in dashboard and reporting totals.

These three dates have different purposes:

Invoice date: when the invoice is issued.
Due date: the deadline by which the customer should pay.
Paid date: when the money actually reaches you. The current invoice tool can mark an invoice Paid, but it does not store a separate paid date.

If the work belongs to a saved project, choose it from Project. Otherwise leave No project selected. The allocation is saved with the invoice and shown in the invoice list and preview.

Add products or services

The form provides three item rows. For each one you use, enter an Item Description and its Amount Before VAT (£). Describe the work clearly enough for the customer to understand what they are paying for, for example “Website maintenance — July 2026”.

Enter the total price for each line rather than a quantity and unit rate: the current form does not have quantity or unit-price fields. Only lines with a description and an amount greater than zero are included. Blank lines, zero amounts and negative amounts are left out.

Simple Books adds the included line amounts to calculate the net total. “Net” means before VAT.

Add VAT where applicable

VAT is a tax charged on certain sales by VAT-registered businesses. Not every business is VAT-registered, and not every sale uses the standard rate. Do not add VAT simply because the field is available.

Choose 20%, 5% or 0% from VAT Rate. The selected rate applies to the whole invoice; Simple Books does not support a different VAT rate for each line. The form starts at 20%, so check it carefully. If you are not charging VAT, choose 0% and make sure the business VAT number is not shown incorrectly.

Simple Books calculates VAT from the net total and then adds it to reach the gross total, which is the full amount the customer owes. For an introduction to the rules and terminology, read What is VAT? and understanding input VAT and output VAT. Ask a qualified adviser or HMRC if you are unsure which treatment applies.

Set payment terms and the due date

Payment Terms explains how long the customer has to pay. The default is loaded from Account, or 14 days if no saved default is available.

When the payment terms contain a number, Simple Books takes the first number as a number of days and calculates Due Date from the invoice date. For example, “14 days” produces a due date 14 calendar days after the invoice date. Changing the invoice date or payment terms recalculates it, and Generate Invoice checks the calculation again.

The Due Date field is editable, but a manual date will be replaced during generation while the payment terms still contain a number. If you need an individually agreed date, use payment-terms wording without a number, enter the date, and review both fields in the preview.

An Unpaid invoice becomes Overdue in Simple Books once its due date is earlier than today. See how overdue invoices work for help following up late payment.

Add payment details and any agreed wording

If Account contains an account name, sort code or account number, Simple Books automatically places the available details under Payment details in the invoice preview. Review them before sending the invoice. The payment terms also appear on the invoice.

The current form has no free-text notes field. Put a useful reference or scope in an item description where appropriate, but do not use it for sensitive information. If the customer needs purchase-order wording or other notes that the form cannot represent, provide that information separately rather than assuming it has been added to the PDF.

Review and save the invoice

Before saving, check the customer, invoice number, invoice date, due date, item descriptions, net amount, VAT rate, VAT amount, total and payment details. Also confirm the selected project if you use project tracking.

Select Generate Invoice. This is the save action for a new invoice: it saves the record with an Unpaid status and creates the Invoice preview. There is no separate Save button. The saved invoice appears under Recent invoices, and its amount and status feed the invoice dashboard totals, status and ageing views, customer statements and financial records. Project details remain attached to the invoice where selected.

A generated invoice can be opened later with Edit invoice. Make your changes and select Update Invoice. If saving succeeds but the related ledger entry cannot be completed, Simple Books keeps the invoice and shows a warning so you can retry or contact support.

Download, print or send the invoice

After generating and reviewing the preview, select Save / Print PDF. Your browser’s print window opens; choose its PDF option to save a file, or choose a printer to print it. If you have not generated a preview first, Simple Books asks you to generate the invoice.

Select Create Email Draft to open your usual email application with the customer’s email address, an invoice subject and a short message. This does not send the email and does not attach the invoice automatically. Save the PDF first, attach it to the draft yourself, check the recipient and wording, then send it from your email application.

Mark the invoice as paid

Generating an invoice records money owed; it does not record money received. When you can see the customer’s payment in your bank or payment service, find the invoice under Recent invoices and select Mark Paid. The button changes to Mark Unpaid so you can correct the status if necessary.

Updating the status removes the invoice from outstanding and overdue totals and includes it in paid totals and customer-statement figures. Simple Books does not ask for or store the payment date, amount, method or bank match in this action, so keep suitable evidence of when the payment arrived. For a focused walkthrough, see how to mark an invoice as paid.

Worked example

A VAT-registered freelance designer invoices a customer for a brand consultation and design work:

Brand consultation: £200.00 before VAT
Logo design: £600.00 before VAT
Net total: £800.00
VAT at 20%: £160.00 (£800.00 × 0.20)
Gross total due: £960.00

With an invoice date of 1 July 2026 and payment terms of 14 days, the due date is 15 July 2026. The customer owes £960.00. The invoice stays Unpaid until the money arrives and the designer selects Mark Paid.

If the designer were not VAT-registered, they would not charge the £160.00 VAT merely because 20% is available in the form; they would select 0% and invoice £800.00, subject to the correct treatment for their circumstances.

Common invoice mistakes

Using the wrong customer details. Check the saved record rather than assuming it is current.
Leaving the suggested 20% VAT rate unchanged. Select the correct rate for your VAT status and sale.
Using a duplicate or unclear invoice number. Keep a consistent, unique sequence.
Entering quantity instead of the line total. Each Amount field expects the full amount before VAT.
Using vague descriptions. State what was supplied and, where helpful, the period or project.
Overlooking the recalculated due date. Check it after changing the invoice date or payment terms.
Assuming Generate Invoice means paid. New invoices are saved as Unpaid.
Assuming the email draft includes the PDF. Attach the saved PDF before sending.
Marking the invoice Paid too early. Wait until you have confirmed receipt of the money.

Summary

To create a clear small business invoice in Simple Books, choose or enter the customer, check the number and dates, add up to three products or services, apply the correct VAT rate and review the payment terms and bank details. Select Generate Invoice to save it as Unpaid and build the preview, then use Save / Print PDF or Create Email Draft to deliver it.

After the customer pays, confirm the money has arrived and select Mark Paid. Keeping the invoice status accurate makes your outstanding, overdue and paid figures—and your customer statements—more useful.