Anyone know why the rising mortgage rate cost is included in inflation calculations? If we use inflation to set our interest rates, and interest rates determine mortgage rates, that turns the whole thing into a mathematical no-no/positive feedback loop. If I recall correctly, Canada includes it in their CPI and the US doesn't.
I don't think interest rates factor directly into CPI. Instead, they push up the cost to produce everything, which in turn pushes up CPI. Mortgage rates specifically push up rents as building owners pass on their higher financing costs. For owner occupied properties, CPI includes owner equivalent rent, which is the rental amount that would have to be paid in order to substitute a currently owned house as a rental property. Rising interest rates do create a positive feedback loop, which is why fiscal and monetary stimulus is playing with fire.
Owner-occupied housing is the hardest thing to do in the CPI. Most things in the CPI are like bananas or whatever, you buy them, you eat them, done. Even things like clothing or washing machines that have a life, basically once you buy them you're intending to use them. But owner-occupied housing has an investment component to it -- people expect that they will sell their house after living in it for years and get a lot of money back; we've built our policies on people getting more money back than they paid (and wonder why housing is becoming unaffordable).
There are a number of approaches that can be used; there's no international standard.
The Aussies just use the cost of new housing (the "net acquisitions" approach) - just like they go to the store and ask how much a pound of bananas costs today and compare with what they cost a year ago, they will go to builders and ask how much a typical house costs and compare that. I don't like this methodology -- for one, it's potentially hard to separate the cost of house and land (and land is purely an investment). And for another, there are plenty of people who have no intention of buying a house for years or decades; a six-month spike in the price of lumber shouldn't jack up the CPI.
The US and the UK use what I would personally use -- the "rental equivalence" method (aka owner equivalent rent). They note that there is a class of people who consume housing services with no investment component at all; that is, renters. At the end of each month, the renter has gotten a month's worth of housing, and no residual value. So this approach is based on figuring out what it would cost if owners were to rent their house instead, and how this would change over time. This is different from just the pure change in rent because the portfolio of owned housing is different; there's less in city centres, owners tend to have larger properties, more houses than apartments, and so on. Presumably whatever owners are paying differently from their rent value represents capital flows; either investments in future property sales, or the payback on having paid off a mortgage.
But
Canada uses what is called "user cost" approach. It's an amalgam of costs that maybe is best though of as trying to approach what a landlord would pay to rent the dwelling to the homeowner -- except their capital costs (capital gains and opportunity cost). The costs are direct household payments on repairs, taxes, insurance and the like, plus depreciation and mortgage insurance cost. The depreciation amount is kind of arbitrary; it's just 1.5% of the value per year. And including mortgage insurance, as as MissingMiddle notes, embeds something that is changed in response to the CPI into the CPI itself. (Note that the US/UK rental equivalence metric doesn't need to include repairs, taxes, etc, because those costs are already automatically included in the rent -- a renter doesn't need to pay separately for repairs or taxes; if the costs go up, their rent will as well to cover the costs.)
I think it's stupid; philosophically, if the appropriate thing to allocate home owner costs is to come up with an equivalent of rental -- and it is -- why use the landlord's perspective, rather than the actual household's perspective? It's like calculating the change in the price of a banana by trying to figure out how much it costs the grocery store to sell it, rather than what the consumer pays to buy it like literally every other price in the CPI. The UK ONS
has a study where they're comparing their housing cost measure with the "net acquisitions" method and a fourth method, the "payments" method, which is basically the "user cost" method less depreciation. But they specifically avoid even calculating a cost measure using our method, "because of the subjectivity involved".