Let me try to give another example than the “two people swapping houses”, which I agree is unrealistic and hard to understand. Hopefully it shall be more relatable whilst still being fundamentally the same.
Let’s say you live and work in place A. You own a home worth 1M, which you could rent for 2k/m. Let’s forget about mortgages, deductions and so forth to simplify, and assume you pay a 25% marginal rent on that 2k fictive income (the inputed rental income is the same as the real rent you could get in our example), thus 500/m.
Let’s now say you get a job offer in place B that looks interesting. B is a bit too far away to commute comfortably, but has the same housing prices. You’re looking for a place nearby.
Problem is, you own your home, so what do you do with it?
You could sell it and buy something in B. But it’s a big effort/commitment until you’re sure you like the job and the place. Plus, between capital gains tax (if your home as appreciated since you bought it), transfer tax, fees, … you would get less housing in B than you have in A despite the prices being the same.
The obvious answer is: I know, I’m going to rent something in B, and rent my place in A. And if I like it after a while, I could look at selling/buying (or not).
So renting for the same housing costs 2k/m as well since the prices are the same. So you pay 2k in rent, but you get 2k in rent from your home in A. After the income tax on the (real this time) rental income, your housing expenses are still 500/m. You’re no better or worse off than before.
Let’s now say inputed rental income is removed. Living in your home in A now costs you 0. Moving to B and renting costs you 500/m.
Again, multiple choices:
- the job only pays 5k/y more than currently. The main reason you were interested was the salary increase. But you would pay 6k/y more in housing! You refuse the job. Now, is it a bad thing? Market theory tells you yes. This is inefficient allocation of resources (namely, you). If they were paying you more, it means you were producing more value in this new job. But the distortion created by income tax pushed you towards the solution that’s less optimal.
- you decide that you would rather keep living in A and do the commute. Again, inefficient allocation of resources. You don’t live in the more efficient place because of the tax distortion. You also don’t vacate your home that could be used by someone that actually needed to live in A. You waste time, money and pollute more on the commute.
- you take the hit and decide to rent. Your material conditions haven’t changed (same housing), but you pay quite a bit more taxes for the “privilege” of now being a renter. One could argue whether this is fair…
I hope this example shows a bit why the inputed rental income can be a good thing, by correcting the inefficiencies/distortions introduced by taxing income.