estimating taxes including sale of rental property acquired in 1031 exchange

The form best used to calculate your estimated taxes for 2024 is the 2024 1040-ES (click the link). There is a worksheet you can use to estimate the total tax. Any tax due that remains unpaid between April 15th and the date you file and pay (if there is any additional tax) will have interest and penalty applied to it.

A faster way to make sure you pay enough tax and do not have an underpayment penalty is to use the following information.

1. Add all taxable income with the exception of the gain on the sale. Figure the tax on that amount from the Tax Rate Schedules on page 7 in the link above.
2. Next,  add 20% of your estimated gain on the trade due to the capital gains tax. Your estimated taxable income in 1. above, plays a factor in determining the capital gains rate that will be used. The maximum capital gains tax rate will be 25% on gain up to the amount of depreciation used on your returns and 20% or less on gain in excess of that depreciation amount.
3. Pay the combined amount of 1 & 2.
   1. See IRS Topic 409 - Capital Gains Rates 
   2. How do I file an IRS tax extension?
   3. Make a Payment Online - You can make a payment at this IRS site or send a payment with your extension.