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If you don't know whether this month went well, it's not a gut feeling, it's four numbers
You set the four numbers you'll check each month to know whether things went well and why, instead of judging it by feel.
By Yodai · Published on September 6, 2026 · Updated on October 12, 2026
Ask the owner of a hair salon, a repair shop, or a home decor store how their month went, and they'll almost always answer with a feeling: "slow," "better than last month," "weird, not sure why." Nobody gives you a number. And if next month feels "slow" again, you won't know if that's just normal or if something's actually broken.
The feeling mixes things that shouldn't weigh the same. One customer who complained takes up more space in your head than the many who left happy. A slow Monday sticks with you even if the whole month went well. It's not just you. Psychologists call this the negativity bias: adults pay more attention to negative information, learn more from it, and rely on it more than on positive information, according to the review of studies by Vaish, Grossmann, and Woodward in Psychological Bulletin. That's why you need to decide ahead of time what you're going to track, not let the feeling decide for you afterward.
Four numbers, not one more
An analytics dashboard can throw a ton of data at you: visits, bounce rate, session length, traffic source. If you look at all of it every month, you don't really look closely at any of it. The approach that works is the opposite, and it's what the college textbook Principles of Marketing, by OpenStax, recommends: instead of a list of hundreds of metrics, stick to a handful of the most useful ones and check them regularly. You pick four numbers, always the same ones, and look at them on the same day every month.
For a business that sells a service or a product, the four that matter are these: how much came in, what each sale earns on average, how many customers come back, and how much it costs you to bring in a new one. With those four, you know whether the month was good and, more importantly, why it was. Three of them are among the key metrics in that textbook. One is sales growth from one period to the next. Another is the percentage of customers in the period who'd already bought from you before. And the third is the cost of acquiring a new customer: what you spend on sales and promotion, divided by the new customers in that period. The same textbook points out that keeping a customer costs less than finding a new one.
- Changes depending on the last customer who called you
- You can't compare one month to another
- It doesn't tell you what to fix, only whether you're happy or not
- Same data, same day, every month: you can compare
- Each number points to a different decision: pricing, promotions, loyalty, advertising
- A few minutes a month, not a dashboard open all day
What I'd pick: Set your four numbers starting this month. The feeling is only good for one thing: a signal to check the numbers earlier than planned, if a month feels very different from the one before.
The four numbers, one by one
- 1How much came in
Your revenue for the month, compared to last month and to the same month last year if you've been open a year. This is the number that tells you if your business is growing, holding steady, or shrinking. - 2What each sale brings in on average
Divide your total revenue by the number of sales. If two months bring in the same revenue but one with half the customers, that average ticket tells you which of the two you'd rather repeat. - 3How many customers come back
Of the people who bought from you this month, how many had already bought from you before. A business that relies on bringing in new people every month spends more and handles a slow month worse than one with customers who return. - 4How much a new customer costs you
What you spent on ads or promotion that month, divided by the new customers it brought in. If that number eats up what the first sale brings in, you're paying to lose that customer.
Where to write them down
You don't need a spreadsheet full of formulas. A note on your phone or in a notebook, with four lines and the date, is enough. What matters isn't the tool, it's using the same one every month, so you can line up one month against another. Once you've got a year of data, line it up against the same month from the year before too. These are two of the comparisons published by Spain's National Statistics Institute (INE) for retail sales: the monthly change, which compares a month to the one before, and the annual change, which compares it to the same month the year before.
- You've stopped judging the month by feel
- You've set the four numbers you'll check every month: revenue, average ticket, repeat customers, and cost per new customer
- You know the day you'll check them: the first Monday of every month
- You have a place to write them down so you can compare one month to another
- The next lesson dives into the first of the four: how much came in this month and what you compare it to
Sources
- Not all emotions are created equal: The negativity bias in social-emotional development. Amrisha Vaish, Tobias Grossmann, and Amanda Woodward, Psychological Bulletin, 2008 (manuscript on PubMed Central, accessed October 2026).
- 2.4 Marketing Plan Progress Using Metrics. Principles of Marketing, OpenStax (Rice University), 2023 (accessed October 2026).
- Retail Trade Indices. Frequently Asked Questions. Spain's National Statistics Institute (INE), accessed October 2026.