I just updated the Estimated Quarterly Taxes template with the IRS’s 2026 rate information. Use the Tiller Community Solutions to install or upgrade to the latest version (1.09).
If you are more familiar than I am with tax rates and standard deductions, please take a moment to unhide the hidden area of the v1.09 template at right and validate the IRS data (especially M32-M36 and K38-P46) to ensure best-effort data-entry mistakes by me 
don’t derail your estimated payments.
Let me know if you see anything amiss.