Social Security benefits are tax-free unless you earn too much income during the year. To know whether you might be subject to such taxes you have to figure your "combined income."
This task is actually quite easy: Simply add one-half of the total Social Security you received during the year to all your other income, including any tax-exempt interest (for example, interest you earned from tax-exempt bonds).
You'll have to pay tax on part of your benefits if your combined income exceeds these thresholds:
If a married couple files their taxes separately, the threshold is reduced to zero—they probably have to pay taxes on their benefits. The only exception is if they did not live together at any time during the year; in this event, the $25,000 threshold applies.
This applies to all types of Social Security benefits: disability, retirement, dependents, and survivors benefits.
How much of your Social Security benefits will be taxed depends on just how high your combined income is.
Individual filers. If you file a federal tax return as an individual and your combined income is between $25,000 and $34,000, you have to pay income tax on up to 50% of your Social Security benefits. If your income is above $34,000, up to 85% of your Social Security benefits is subject to income tax.
Joint filers. If you file a joint return, you have to pay taxes on up to 50% of your benefits if you and your spouse have a combined income between $32,000 and $44,000. If your income is more than $44,000, up to 85% of your Social Security benefits is subject to income tax.
If you earn enough money for your benefits to be taxable, you could end up paying the highest income taxes in the country. Here's why: Every dollar you earn over the 85% threshold amount will result in 85 cents of your benefits being taxed, plus you'll have to pay tax on the extra income. So for every dollar you earn over the 85% threshold, you'll end up paying tax on $1.85. If you're in the 22% bracket, this works out to a 40% tax rate (22% x 1.85 = .407).
Calculating the exact amount of tax that must be paid on Social Security benefits can be quite complicated. IRS Publication 915, Social Security and Equivalent Railroad Retirement Benefits, contains detailed instructions and a worksheet you can use.
If you plan to work after the normal retirement age, you should consider putting off claiming your Social Security benefits. If you wait until after your full retirement age to claim Social Security retirement benefits, your benefit amounts will be permanently higher.
Your benefit amount is increased by a certain percentage each year you wait up to age 70. After age 70, there is no longer any increase, so you should claim your benefits then even if they will be partly subject to income tax.
Once you start receiving Social Security benefits, to keep your income below the applicable threshold, or at least as low as possible, you should:
The tax laws encourage retired people to "live in sin"—that is, without benefit of marriage. A couple increases the amount of income they can earn without being taxed on their Social Security benefits if they aren't married and file their taxes separately. Each will be entitled to earn $25,000 in combined income without paying tax on their benefits, for a total of $50,000 of income without extra taxes. In contrast, a married couple can earn no more than $34,000 in combined income without paying extra taxes. However, a married couple can get the same treatment as singles if they live apart part of the year and file their taxes separately.
For more information on Social Security, refer to Social Security, Medicare & Government Pensions: Get the Most Out of Your Retirement & Medical Benefits, by Joseph L. Matthews and Dorothy Matthews Berman (Nolo).