@starlit
Regarding land values, is the NTA Rosenka site actually the gold standard?
That site is only relevant to inheritance and gift tax. It is not directly relevant to property tax, which is assessed by municipalities.
It is often said (e.g.,
here) that land can be valued in five different ways, which is a reference to:
- the property tax value (固定資産税評価額), determined by municipalities;
- the inheritance/gift tax value (相続税路線価), determined by the NTA;
- the standard value (基準地標準価格), determined by prefectures;
- the official public value (公示地価), determined by the Ministry of Land, Infrastructure, Transport and Tourism; and
- the market value.
For the purpose of calculating property tax values, municipal governments create their own price maps (路線価), which look similar to the NTA's 路線価 maps, but do not contain the same values. You may be able to view a municipality's price map on its website, but the most convenient option is usually to use an aggregator like
this site, which collects price maps from all municipalities.
It's important to note that these municipal price maps are only the
starting point when determining the property tax value of a piece of land. The actual property tax value is determined by municipal staff after considering the individual characteristics of the property. And this final value is not public. Only the owner of the property and a few other types of interested parties (heirs, etc.) can ask to see it.
I've always understood 80% of market price to be the recommended value for calculation
Inheritance/gift tax values are generally said to be ~80% of the official public value, and property tax values are generally said to be ~70% of the official public value. But note that these rules only apply to the land. Property tax is levied on both the land and the building, so you will need to consider the building's property tax value if you are trying to estimate the overall property tax liability. Buildings are valued by appraisers working for municipal governments based on extensive rules set by the Ministry of Internal Affairs and Communications (固定資産評価基準), but the values of individual buildings are not published.
does the 12,000,000 JPY deduction exist only on the acquisition
That deduction applies to the tax value of the building (not the land) for the purpose of calculating the prefectural real estate acquisition tax due at the time of purchase. There are other deductions applicable to the tax value of the land.
Tokyo's prefectural tax bureau has a lot of good information about how real estate acquisition tax is calculated
here, including a tax calculator
here.
is there an equation similar to land where even in the first year for a new house, the assessed value will be lower than the actual construction costs?
The value of the building for property tax purposes will be determined by municipal employees based on the plans and an on-site inspection once construction has finished (applying the MIC's rules). There are an enormous number of variables, but architects/house builders are generally familiar with those variables and should be able to give you a useful estimate.
In terms of yearly depreciation on wooden residential properties, is this equation fairly accurate?
That is the equation used for income tax purposes. It is not useful for property tax purposes. The property tax value of a building depreciates according to a declining-balance method prescribed by the MIC.
This site provides a nice explanation of the rules applicable to changes in the value of timber-frame residential properties, as well as a depreciation calculator. And, of course, neither the income tax formula nor the property tax calculations tell you anything about how the actual market value of the property will change over time.
