Why it works differently
When you are on a traditional paycheck, your income is already a number on a document somebody else produced. When you work for yourself, your income has to be established from your own records.
That means the picture a lender sees is the one your tax returns paint. If you have been deducting aggressively — which is legal, and often sensible — the number on your return may be lower than what you actually take home. It is worth knowing that before you apply rather than during.