Fortunately, no. The amount of the benefits includible in gross income may be zero, somewhere between zero and 50%, or somewhere between 50% and 85%; 85% is the maximum taxable percentage. The exact amount depends on the amount of your net benefits, your tax-free interest from municipal bonds, and your overall income.
A 12-month period ending on the last day of any month other than December. Partnerships, S corporations, and personal service corporations are limited in their choice of fiscal years and face special restrictions.