To calculate the Qualified Business Income (QBI) Deduction in Excel, you need to perform the following steps:

- Determine your eligible QBI amount: This is equal to the net income from your business minus any allowable deductions for that business.
- Determine your taxable income: This is equal to your total taxable income minus any taxable deductions.
- Determine your QBI Deduction limit: The QBI Deduction limit is the lesser of 20% of the QBI amount or 20% of taxable income.
- Calculate the QBI Deduction: To calculate the QBI Deduction, simply subtract the limit determined in step 3 from the QBI amount determined in step 1.

Here's an example formula in Excel:

=MIN(0.2 * (A1 - A2), 0.2 * (B1 - B2))

Where:

- A1 represents the QBI amount
- A2 represents the allowable deductions for that business
- B1 represents the taxable income
- B2 represents the taxable deductions

This formula calculates the QBI Deduction by determining the limit and then subtracting it from the QBI amount.