What if I don't know my expected gains, income, and losses for 2026?

[Mike9241 · Accepted solution]

your choice is to risk penalties for underpaying estimated taxes or paying in too much unless you use the only safe harbor you can know for sure. That's 100% of your 2025 federal income taxes. This rises to 110% if your 2025 Adjusted Gross Income is $150,000 or more ($75,000 if married filing separately) 

There are other safe harbors like 

90% of 2026 tax or owing $1,000 or less after subtracting any withholding from your 2026 tax liability. However, you won't know this for sure until 2027.

you do have the option if you think your taxes will be lower for 2026, to adjust the estimated tax payments downward as the year progresses.