People who rent out their houses on Airbnb stand to make, on average, less than half of what they charge, new figures based on the company's data and checked by the Australian Tax Office (ATO) show.

Apartment-owners fare only slightly better, likely to make a little over half the price they tend to charge, after paying income and Capital Gains Tax when they finally sell their property.

And if either group doesn't declare their participation in the sharing economy in a bid to avoid tax then they're "likely to receive a 'please explain' letter from the ATO," warns Mark Chapman, director of tax communications at H&R Block.

"[The ATO] is able to data-match rental income with third party data, not least the Airbnb website itself, which discloses information about you and your property, which the ATO can then match with your tax return," he says.

"Bear in mind too that the ATO shares information with State Revenue Offices. That has led the Tasmanian SRO to attempt to levy land tax on some Airbnb renters in that state - a legally dubious challenge but one that other states could follow if a precedent is set."

The calculations were done by officers of the Our Strata Community, Our Choice (OSCOC), an organisation that is lobbying the NSW Government for apartment buildings to be allowed to continue to decide themselves - by a 75 per cent majority vote - whether to permit Airbnb to operate in their buildings. All their figures were run past by the ATO as well as H&R Block and then reworked to take in their amendments.

But the final results stunned them. "We were shocked to find that people renting out their homes on Airbnb and presumably other organisations too like Stayz will make so little profit on it in the long term," says Michael Mangan, OSCOC chairman.

"I think a lot of people haven't really figured that out yet. Most people won't make much profit after tax and then, on top, they'll have cleaning costs, the costs of making good any wear and tear on their property and any damage. In some areas where the value of property has gone up by a lot over the past couple of years, we actually found some people, when they come to sell their home, making a loss."

The figures are based on average wage-earners, living in average priced homes whose value has risen by an average percentage, and letting out rooms, or their whole home, for an average 28 days a year, on Airbnb-supplied numbers, and charging an average $160 a night.

Those in houses were discovered to have a $1462 income tax bill in 2016 and owe another $1352 in capital gains tax if it were sold. It meant they'd end up receiving just $60.17 a night.

Apartment-owners did only marginally better, making $89.91 a night.

An ATO spokesman said: "If you earn money from renting out a room or house you need to declare it because it counts as assessable income. Any money earned through accommodation sharing, where you rent out all or part of your house or even a car space, should be included in your individual tax return as rental income.

"We are focused on supporting those participating in the sharing economy through accommodation rental by making it easier for them to understand their obligations."

An Airbnb spokesman declined to comment on the figures but said that, while every host's financial situation was different, the company recommends they seek advice from their accountant or a tax professional.

"The average income for Australian hosts is just $5000 a year, and while this may not sound like a lot, we know the impact can often be life changing," he said. "Our hosts tell us this modest extra income helps pay off the mortgage, cover bills and household expenses. Others list their home to pay for their own holiday away with the family once or twice a year.

"Many of our hosts make a modest income from Airbnb, which will of course be offset by the deductions they are entitled to. We make it easy for hosts to declare their income by proactively providing them with a summary of earnings every year before tax time."

But Chapman has urged anyone contemplating, or actively renting out their homes or rooms on services such as Airbnb, to sit down and work out the financial implications early on.

"As time consuming and difficult as it may be, take the time at the start to work out your post-tax financial returns - not just from the rental itself but over the whole life of your ownership of the property," he advises. "That way, you will be walking into your Airbnb arrangement with your eyes open and will avoid any unpleasant financial shocks down the road."

Unit rented out on Airbnb in 2016 - According to Airbnb numbers

If last year you were an average wage earner in NSW ($80,132) who owned and lived in an average apartment in Sydney (worth $711,256), which increased the average value that year (6.3 per cent or $42,367), and you let it out for the average number of days on Airbnb (28 days), and you received the average amount of income from that ($4500), you would be liable for:

• A $1462.50 income tax bill this year
• Another $519.93 capital gains tax bill when you sold it

In order to comply with tax law, you would actually have a tax bill of $1982.43 against an income of $4500, which works out as a profit of just $2517.57, or $89.91 per night it is rented out.

Assumptions:

* Assuming unit held for 12 months, by individual/s (not superannuation), apply 50% CGT exemption

House rented out on Airbnb in 2016 - According to Airbnb numbers

Issue:

If last year you were an average wage earner in NSW ($80,132) who owned and lived in an average home in Sydney (worth $1,123,991), which increased the average value that year (10.7 per cent or $108,532), and you let it out for the average number of days on Airbnb (28 days), and you received the average amount of income from that ($4500 ), you would be liable for:

• A $1462.50 income tax bill this year
• Another $1352.72 Capital Gains Tax Bill when you sold it

In order to comply with tax law, you would actually have a tax bill of $2815.22 against an income of $4500, which works out as a profit of $1684.78 a year, or $60.17 per night that you rent out your house, and a tax rate of 87 per cent.

Assumptions:

* Assuming house held for 12 months, by individual/s (not superannuation), apply 50% CGT exemption