Best tax estimator besides IRS?

I need to make a supplemental 2025 tax payment before January 15th to avoid underwithholding penalties and I'm just trying to do a quick calculation but the IRS tool is down for maintenance for the next couple of weeks.

Are there other good tools that are quick and easy to use? If not, I'll have to manually ballpark it myself (I don't need something 100% accurate. Just a ballpark, hopefully to +/- 5% is sufficient)

I have my W-2 info. I file as HoH and will claim the SALT deduction and mortgage interest for 2025, so hopefully the estimator will be able to handle these deductions as they will be substantial for my case. I'll be maxing out both categories. I have over $40k in property and state income taxes and a mortgage over $750k. I've never itemized deductions before, but IIUC, the math is just that instead of subtracting the HoH standard deduction from my wages, I subtract the itemized deduction instead, and that's the only thing that changes…