Small businesses usually have more useful data than they realise and use almost none of it. Sales records, till or invoice history, and the debtors book together answer the questions that matter most: what actually sells, who actually buys, which customers return and which cost you money. None of that needs a new system.
Four questions your existing records can answer this week.
What actually sells, and what it earns
Rank your products or services by revenue, then rank them again by margin. The two lists are rarely the same, and the difference tells you what to promote and what to drop.
Almost every business finds a small number of lines carry it. Concentrating on those rather than broadening is frequently the entire strategy.
Who buys, and who comes back
Sort customers by what they have spent over a year and by how often. The pattern shows where your revenue really comes from and how dependent you are on a few relationships.
Then look at who stopped. A customer who bought regularly and has not for months is a silent loss, and a call asking why is the cheapest research available to you.
When things happen
Sales by month, week and day of week tell you when to staff, when to order and when cash will be tight. Seasonality that feels vague becomes plannable once it is written down.
Pair that with your debtors book: the average days customers take to pay moves before revenue does, which makes it the earliest warning available.
Keep it simple and lawful
A spreadsheet updated weekly beats a system nobody opens. Accounting software that already holds your invoices can produce most of this without any extra work.
Customer information you hold and analyse carries obligations under the Protection of Personal Information Act, overseen by the Information Regulator: collect only what you need, keep it secure, and have a lawful basis for using it, including for marketing.
Frequently asked questions
Do I need new software to use my data?
No. Sales records, invoice history and your debtors book answer most questions, and accounting software already holds them.
What is the most revealing thing to check?
Ranking products by revenue and again by margin. The lists differ, and the difference shows what to promote and what to drop.
What should I do about lapsed customers?
Identify who bought regularly and stopped, then ask why. It is the cheapest research available to a small business.
Which number gives the earliest warning?
Average days customers take to pay, which moves before revenue does.
What obligations come with customer data?
Collect only what you need, keep it secure, and have a lawful basis for use including marketing.
Originally published in June 2018. Updated September 2026 into guidance on using the data a small business already holds.
