The total tax levy to be collected is the sum of the local budget and the budgets of the school board and county board. This figure is divided by the total assessments in the township to produce the tax rate. That tax rate is then applied to individual assessments.
The 1st half of your tax bill is estimated, and equal to half of the total prior year taxes. It is estimated because the rate cannot be computed until all budgets have been approved; budget approval occurs in June. The 2nd half tax bill is computed by applying the new tax rate to the current year assessment, then deducting the amount billed in the 1st half.