Annualizing

Annualizing means:
the required method whereby a taxpayer changing from one tax year end (fiscal tax year) to a different tax-year end annualizes the income for the resulting intermediate short period for the purpose of calculating the income tax liability. In effect, this method calculates what the tax would be if income had been received for an entire year at the same rate as during the short period. This tax is then divided by 12 and multiplied by the number of months in the short period. Annualizing prevents any income earned during a short period from being taxed at lower rates. Former IRC (check if this IRC provision is current here) §443.

See the entries Income Tax and State Income Tax in the American Encyclopedia of Law.