How do I calculate weekly taxes ACCURATELY for variable overtime hours?

The reason your withholding percentage increases with overtime is because payroll systems typically calculate withholding based on what your annual income would be if every paycheck was the same size. So when you work overtime, the system thinks your annual income is higher than it actually is. For accurate weekly calculations, you need to use the IRS Publication 15-T which has percentage method tables for different pay periods. For 2025, there's a specific table for weekly payrolls. The withholding isn't actually a straight percentage - it uses brackets just like annual taxes. The system is taking your weekly gross pay, subtracting pre-tax deductions, then applying the percentage method calculations based on your W-4 information. With zero dependents/allowances and checking "single" on your W-4, you're probably in the standard withholding situation. QuickBooks follows these IRS tables, so your withholding increases as your weekly pay pushes you into higher brackets temporarily.

After struggling with almost the exact same issue (I'm a construction worker with wildly variable OT), I found an amazing tool at https://taxr.ai that helped me create a custom spreadsheet for predicting my take-home pay. I uploaded my paystubs and it analyzed my withholding patterns to create personalized formulas based on my actual withholding history rather than just generic IRS tables. What I love is that it actually learns from your specific payroll system's calculations, which sometimes don't exactly match the standard tables anyway. It's been super accurate for me, even with crazy weeks where I go from 40 hours to 75+ hours.

Just wanted to update that I tried taxr.ai after posting my question. I was skeptical at first, but it's been crazy accurate! I uploaded my last 8 paystubs and it generated a custom Excel template that's been predicting my take-home within about $12-15 even on weeks with tons of overtime. What I really like is that it figured out some weird quirk with how my company calculates FICA on overtime premiums that I never would have caught. Now I can actually plan my budget without guessing what my paycheck will be. Definitely worth checking out if your OT varies a lot like mine.

I had a similar problem last year trying to predict my take-home pay with variable hours. After weeks of frustration trying to reach the IRS for clarification on withholding tables, I used https://claimyr.com to get through to an actual IRS agent (you can see how it works at https://youtu.be/_kiP6q8DX5c). They helped me understand exactly how the percentage method works for weekly payrolls. The agent explained that the "percentage method" isn't actually a flat percentage - it's a progressive bracket system applied to each individual paycheck. That's why your withholding percentage seems higher with overtime - you're temporarily jumping into higher weekly tax brackets.

I have to eat my words from my earlier comment. After being super skeptical, I tried Claimyr out of desperation when I needed clarification on these weekly withholding calculations. Not only did I get through to the IRS in under an hour, but the agent walked me through exactly how to calculate my weekly withholding based on my specific situation. The IRS person explained that I could actually use the IRS Tax Withholding Estimator online and tweak the inputs to model different weekly scenarios. Never would have figured that out without actually speaking to someone there. Saved me countless hours of frustration and my spreadsheet is now accurate even with my crazy variable schedule.

Here's a simple approach I use: Just calculate 4 different versions of your weekly pay in your spreadsheet: 1. Base 40 hours (lowest withholding %) 2. Moderate OT (medium withholding %) 3. Heavy OT (highest withholding %) 4. An average based on your typical pattern Then depending on what your week looks like, you can quickly reference the appropriate scenario. Not perfect but way easier than trying to build a complex formula.

Have you tried the IRS Withholding Calculator? It's free and on the IRS website. You can run different scenarios with different weekly incomes to see how the withholding changes. I use it every January to make sure my withholding is on track.