If you have taxable income in addition to your annuity or if you or your spouse can be claimed as a dependent on another person's tax return, you may want to claim fewer allowances.
If you itemize deductions on your return, have tax-free income, or have any tax credits available, you may want to claim additional allowances.
If either of the above two situations applies to you, contact the Internal Revenue Service for information on the correct number of allowances
you should claim based on your financial situation. Look for Publication 721, "Tax Guide to U.S. Civil Service Retirement Benefits," on the IRS website.