A P&L statement can add up perfectly and still tell a misleading story if the numbers going into it aren't put together carefully. These are the mistakes that come up most often in small business bookkeeping.
Mixing personal and business expenses
A single personal purchase run through the business account distorts the expense total for that category, and doing it repeatedly makes the whole statement unreliable for actually understanding the business's costs.
Recording revenue when invoiced, not when paid — without tracking the difference
If you count a sale as revenue the moment you invoice it, but the client hasn't actually paid yet, your P&L can show a profitable month while your bank account tells a very different story. Track both invoiced and collected figures if this applies to your business.
Forgetting irregular expenses
Annual software renewals, insurance premiums, or equipment maintenance that happen once or twice a year often get left out of monthly tracking, making regular months look better than they really are once those costs are averaged in.
Not separating one-time events from ongoing operations
A one-off grant, a large equipment sale, or an unusual refund can make a single month's P&L look dramatically different from normal — worth noting separately rather than letting it blend into the regular trend line.
Never comparing to a previous period
A P&L statement in isolation tells you where you are. Compared to last month or last year, it tells you where you're heading — and that direction usually matters more than any single number.