A year, not a month

With irregular income the most expensive mistake is to treat a good month as the new normal. A good month is not an income; the year is. To find what you really earn, add up every month and divide by twelve.

Dana's twelve months come to 430,000 UAH (860 lessons × 500). The average month is 430,000 / 12 = 35,833.33 UAH, before taxes. That is the figure a year-long decision — a lease, a loan — has to fit, because rent falls due in July as well as in March.

The average is deliberately lower than the best months feel: it already carries the thin summer inside it. Always work from the whole table, not from the month you remember best.

With a seasonal income it pays to count how many months sit below the average. For Dana, five of twelve months (December, January, June, July, August) were below 35,833.33 UAH; the other seven were above it.

That is the quiet trap of an average: most months feel richer than it, because a few very thin months — here the summer — pull it down. In spring, when seven months in a row beat the average, the average looks pessimistic and a good month looks like proof you can spend more.

The opposite is true. The average is low precisely because July exists, and July is exactly what it has to pay for. The number that feels too cautious is the one that keeps the year solvent.

A year-long commitment — rent, a loan, a subscription — is paid every month, good and bad alike. So it must rest on the yearly average, after taxes, not on a single month.

• The best month (March, 52,000) is the surplus you save, not the income you spend.
• The median (38,000) describes a typical month, but half the year earns less, so it still overstates what you can commit to.
• The worst month (July, 15,000) is over-cautious on its own, as long as the summer gap is covered from the good months.

The average, 35,833.33 before taxes, is the one figure that fits all twelve payments. Take taxes off it first, then decide what a fixed monthly cost can be.

A single strong month tells you almost nothing about the next eleven. Dana's 52,000 UAH March was followed by a 15,000 July. Raising monthly spending by 45% because one month ran 45% above the average would commit the whole year to a level only one month reached.

Spending is set from the yearly average; the surplus of a good month is kept, not absorbed into a higher standard of living. A rise in spending is permanent, but a good month is temporary — so the good month funds the thin months, and only a lasting rise in the average (more lessons, a higher rate, once it actually shows in the data) justifies spending more.