This is a simplified view of  local property taxes.

Tax rates are set via a process defined in NH statutes and administrative rules.

This (200 page) manual is a good place to start if you're interested in more detail:

https://www.revenue.nh.gov/mun-prop/property/documents/asb-manual.pdf

 

Every year, NH town and school districts determine their budgets. 

The county budget is determined by the state representatives of the county.

The budget sets an "appropriation" - the amount the governmental unit ( town, school or county ) authorizes to spend for services.

All of the property in each town is cataloged and assessed.

Assessments are an estimate of the value of each property, performed by professional assessors. 

The tax rate is set by the NH Department of Revenue Administration.

It is basically, for each governmental unit:

                     ( appropriation - estimated revenue) / total value of property

 

As an example, these are the tax rates for a typical town in Rockingham County:

Year Municipal Tax School Tax State Tax County Tax Rate
2017 $3.62 $14.85 $2.45 $1.19 $22.11

Tax rates are defined as being per $1000 of property value. 

The tax a property owner pays is basically:

                 (value of property, in thousands) times (tax rate)

So a $100,000 property with these rates would be charged $2211    in taxes.

Bear in mind, this is very simplified.

There are other factors in the calculation of the tax on a given property such as whether the property is under "current use" ( a reduced tax is levied as an incentive for not subdividing and building).

Property owners may also have certain exemptions that reduce the tax - for example , many towns provide exemptions for elderly owners, and for veterans.