NOI Calculator: Net Operating Income Explained
1. Short answer
NOI (net operating income) is annual rent minus operating costs. It is what the property produces from letting, before financing and tax.
NOI = annual rent − operating costs
An apartment with € 17,700 of annual rent and € 6,626 of operating costs has an NOI of € 11,074. Unlike yield, DSCR or LTV, NOI is not a percentage but an amount, and that amount is the numerator under almost every other metric.
2. Why NOI is the figure that matters most
NOI is the hinge of the whole calculation. It reappears as the numerator in:
- net yield (NOI ÷ total investment)
- cap rate (NOI ÷ market value)
- DSCR (NOI ÷ interest + principal)
- ICR (NOI ÷ interest)
One optimistic assumption in NOI therefore flows into four metrics at once. Understate maintenance by € 2,000 and your net yield, cap rate, DSCR and ICR all look better than they are, and you find out when the invoices arrive.
What it does not include:
- no interest or principal: NOI describes the property, not your loan
- no income or corporation tax
- no depreciation
- no value-adding capital works (those belong to your investment, not to operations)
3. Which costs belong in it
This is where most calculations go wrong. The rule of thumb: costs that recur while you own the property belong in it. One-off spending does not.
Start with the income side, where three terms need keeping apart. Contracted rent is base rent times twelve, uncorrected; that is the numerator of gross yield. Collected rent, or effective gross income, is what survives voids and bad debt. Voids and arrears are therefore not a cost line but a reduction of income: they come off the rent before any expense is applied. The distinction looks like bookkeeping, but it decides the denominator of your NOI margin and the basis of a percentage management fee.
| Item | In NOI? | Why |
|---|---|---|
| Maintenance | Yes | Recurs while you own |
| Service charges | Yes | Monthly obligation |
| Insurance | Yes | Annual |
| Local taxes | Yes | Annual |
| Management | Yes | Even if you do it yourself |
| Voids and bad debt | Yes, but off the rent | They reduce income; they are not a cost line |
| Interest | No | Belongs to financing, not the property |
| Principal | No | Equity build-up, not a cost |
| Acquisition costs | No | One-off; already in your investment |
| Renovation | No | Adds value; that is investment |
The item most often missing is management. If you self-manage, the temptation to enter zero is strong. But a buyer will price it in, and your time is not free. Use 4% to 7% of rent. If you agree a percentage, check the basis: a managing agent normally bills on rent collected rather than rent contracted, so the fee falls automatically when you raise your void assumption.
Watch the unit as well. Some items you know as monthly figures (service charges, communal utilities, a maintenance sinking fund, insurance) and others as annual ones (local property taxes, ground rent). Mixed into a single total, a factor of twelve slips in easily, and it rarely announces itself because the result still looks plausible. Convert every line to an annual figure before adding them up.
4. Worked example
The same apartment as on the other pages: 75 m², mid-sized city, let at € 1,475 a month.
Income side first, then the costs.
| Item | Per year |
|---|---|
| Contracted rent (12 × € 1,475) | € 17,700 |
| Void allowance (3%) | − € 531 |
| Collected rent | € 17,169 |
| Maintenance (1% of purchase price) | − € 2,850 |
| Service charges | − € 1,560 |
| Insurance | − € 320 |
| Local taxes | − € 480 |
| Management (5% of contracted rent) | − € 885 |
| Total operating costs | − € 6,095 |
NOI = 17,169 − 6,095 = € 11,074
| Metric | Value | What it means |
|---|---|---|
| NOI | € 11,074 | What the property produces annually from letting |
| NOI margin | 64.5% | Just over 64 cents of every euro collected remains |
| Operating expense ratio | 35.5% | What ownership consumes each year |
Mind the denominator of the margin. NOI margin divides NOI by collected rent, not by contracted rent. That is not arbitrary: with voids already reflected on both sides of the fraction, the margin measures the cost side cleanly instead of quietly also grading your void assumption. It also yields two figures that add to exactly 100%. Divide by contracted rent by mistake and you get 62.6%, a number that measures two things at once.
That margin is a useful check on your own assumptions. Above 75% and you have almost certainly forgotten an item.
5. What counts as a good NOI margin?
| Range | What it usually signals |
|---|---|
| above 75% | Almost always a missing item. Check maintenance, management and vacancy |
| 60% – 75% | Typical for houses without service charges, or low ones |
| 50% – 60% | Normal for apartments with an active owners' association |
| below 50% | High fixed costs, or an input error; see below |
The margin says more about the type of property than its quality. An apartment with a well-funded reserve has a lower margin than a house, but major works are already covered.
Each end of that table calls for a different check. At the top it is nearly always a forgotten item, usually the maintenance provision or the insurance. At the bottom it is rarely the property at all: look first for interest that has crept in among the operating costs, or for an annual amount sitting in a monthly field. On ordinary residential stock a margin that low is rare; an input error is not.
6. Three mistakes that distort the number
Interest included. The most common error, and it makes NOI unusable for DSCR: interest then sits in both numerator and denominator.
Management at zero. See above. On € 17,700 of rent that is € 885, nearly 8% of your NOI.
Using asking rent instead of received rent. Voids, rent loss and arrears come off. NOI should describe what actually arrives. Run the calculation on € 17,700 instead of € 17,169 and NOI lands at € 11,605: 4.8% too high, and that error carries straight through to DSCR and therefore to what a lender is willing to advance.
7. Run your own numbers
Enter your own figures above. To take NOI through to cash flow, DSCR and multi-year operation with rent indexation, the BRIX Calc rental calculator does it in full.
8. Frequently asked questions
Is NOI the same as net rental income?
Yes: two names for the same amount: annual rent minus operating costs, before financing.
Does major maintenance belong in NOI?
Only as an annual provision. Deducting a € 20,000 roof replacement in full in one year makes that year's NOI useless for comparison. Reserve an annual amount instead, or run it through the service charge.
Why is principal excluded?
Because repayment is not a cost but equity build-up: the money does not disappear, it moves from your bank account into your stake in the property. It does affect your monthly cash position: cash-on-cash is the right figure for that.
Do acquisition taxes belong in NOI?
No. Stamp duty, transfer tax, notarial and agency fees are one-off costs of buying. They belong in the total investment, which is the denominator of net yield and of cash-on-cash return. Put them among the operating costs and year 1 is artificially depressed while every later year is overstated, leaving the two years incomparable.
What is the difference between NOI and cash flow?
NOI stops before financing; cash flow runs on to your bank account. Cash flow is NOI minus interest and minus principal. Two properties with an identical NOI can therefore end up worlds apart, purely on the financing underneath them. That is also why NOI is the right figure for comparing assets and the wrong one for judging affordability.
How does NOI relate to cap rate?
Cap rate is NOI divided by market value. If you know the cap rate comparable properties trade at, you get a value indication: value ≈ NOI ÷ cap rate. At an NOI of € 11,074 and a market cap rate of 4%, that is roughly € 277,000.
Does NOI change if I refinance?
No, and that is the point. NOI describes the property, not your loan. Refinancing changes your cash flow, DSCR and cash-on-cash: NOI stays the same.