If the annuity was purchased with pre-tax dollars, then the entire distribution will be taxable, however, non-qualified annuities are typically purchased with after-tax money.
Often (not always), when the taxable portion is not determined (reported on the 1099-R), then some portion of the distribution is a return of after-tax money. You should contact the issuer to make sure you have a non-qualified annuity.
Qualified annuities (such as annuities in an employer-sponsored retirement plan or an IRA) are typically purchased with pre-tax money, so withdrawals are fully taxed as ordinary income.
Non-qualified annuities are typically purchased with after-tax money. Distributions are taxable upon withdrawal, but only the earnings portion of the distribution is taxed.
