Easy way to calculate Income and Tax with Progressive Tax Structure when starting above $0.

Here’s my scenario:

I need to regularly recalculate taxes for thousands of individuals who are paying taxes in a tiered jurisdiction. To make it easy, say it’s 6% up to 75,000 in earnings and then 8% from 75,000 to 85,000. 85k is the maximum income taxed.

This is easy to do when starting at zero and calculating annual income. My issue is this is mid-year when they don’t start at 0 earnings.

I’ve largely got this with a massive amount of nested “IF” statements but it seems inefficient.

Every example I’ve found is annual calculations that start at zero.

To add to the complication, many of these people will have multiple paychecks on the same day and this income is sourced income. Meaning, only a portion of the income itself is going to be taxed to the jurisdiction. I can mostly account for that in any formula.