Finding the correct numbers for the "Active Duty Pay Deduction" for my Missouri State Taxes?

On line 17 of your Form MO-1040, you're allowed to claim a deduction for the entire amount of military income earned as a member of any active duty component of the Armed Forces of the United States that's been included in your federal adjusted gross income, and not previously taken as a deduction.

And, according to LINE 18 - RESERVES AND INACTIVE DUTY MILITARY DEDUCTION in the form instructions in the link above,

Beginning with tax year 2020, military personnel may deduct a portion of their income earned from the following sources from their Missouri adjusted gross income:

• National Guard Inactive Duty Training (IDT)

• National Guard Annual Training (AT)

• Reserve components of the Armed Forces

In tax year 2020, the deduction amount is 20% of such pay.