Effective gross income is the rent and other income a property actually brings in over a year, after you subtract the rent you lose to empty units and uncollectible payments. It starts from gross potential rent, the figure you would collect if every unit were full and every tenant paid in full, and then trims it down to a number you can plan around.
The whole point is honesty about the top line. Gross potential rent is a best case that almost never happens for a full year, so effective gross income is the realistic revenue you carry into the rest of the profit-and-loss statement.
In practice
Say you own a fourplex where each unit rents for $1,200 a month. That is $4,800 a month and $57,600 a year in gross potential rent if nothing ever goes wrong. Now subtract a vacancy and credit-loss allowance. One unit sits empty for two months during a turnover, costing $2,400, and a tenant skips out owing $900 you never recover. That is $3,300 of lost rent.
Then add the other income the building throws off: $600 a year in pet rent and $480 in coin laundry, so $1,080 on top.
Effective gross income = gross potential rent − vacancy and credit loss + other income = $57,600 − $3,300 + $1,080 = $55,380
That $55,380 is the number every downstream metric should start from, not the $57,600 the rent schedule implies. The gap, $2,220 in this case, is exactly the cushion a flattering listing leaves out.
Why it matters to a small landlord
For a 1-to-10 unit owner, effective gross income is where most overpaid deals start to go wrong. A seller hands you a pro forma built on full occupancy and zero bad debt, the cap rate looks fine, and you only find the truth after closing. Building the top line yourself from a realistic vacancy rate is the step that keeps a too-optimistic revenue figure from inflating every return number that follows. Get this line honest and the rest of the underwriting tends to stay honest too.
Effective gross income is the bridge between a few related terms worth knowing. Your vacancy rate is the assumption that does most of the trimming, the result feeds straight into net operating income once you subtract operating costs, and it is the line a careful pro forma gets right while a sales sheet quietly rounds it up. Treat it as the realistic top of the page and the numbers below it stay believable.