I have read the different posts on this and still am not clear on what to with estimated tax payments to avoid a penalty in 2025. I am making the 4 regular and equal 2025 payments based on the 100% rule for last year's - 2024 taxes. At the end of August I will receive the proceeds and capital gains on the sale of a rental property. So my question is should I boost my September 15th estimated tax payment to reflect the estimated incremental taxes of about $20K on this gain?
Yes that would work. You can just cross out the amount on the 1040ES and write in a new amount or pay the IRS directly online.
If your AGI was less than $150,000, and by Jan15 2026 you will have paid in last year's tax as you say (equal payments), you won't get a penalty.
You may pay more estimated tax only to reduce the amount due on April 15th.
Our 2025 AGI will be more than $150K due to the rental property sale. Does that affect this?