Is there a way to figure what our additional tax would be if we took a payment from an annuity account and decided not to pay it back but keep it as additional income?

You could use the TurboTax calculator TaxCaster.  It is currently available for tax year 2023 but will give you a close estimate of taxes owed or a tax refund for 2024.

Go to this TurboTax website for TaxCaster - https://turbotax.intuit.com/tax-tools/calculators/taxcaster/

Great thank you so much for the information. I will try it this weekend.