The mileage deduction is based on business miles driven.  The business mileage deduction for 2019 was  .58 per mile. As an example of the deduction if you drove 10,000 miles your deduction would be $5,800 ( .58 x 10,000)

Hello, the miles driven was actually about 18k miles. So the deduction should be about $10k taken off, however the deduction showed at the top only dropped about $3k

Business miles are not a dollar for dollar deduction. Look at your form. You might have gotten a $3000 reduction from the 10,000 miles.

If I drove 10k miles for business last year, it’s .58 a mile, so that’s $5800, do you get the full amount deducted from your taxes or only a percentage?

If you drove 10K miles for business, you would get a business expense for $5800.

The business expense would reduce your business earnings (or increase your business loss) by $5800. If you have a Schedule C business it appears on Line 9 of the Sch C. How much the business expense is worth to you depends on your tax rate. If your income is positive and you are in the 12 percent bracket, this would save you roughly $1,566 (12 percent income tax and about 15 percent SE tax). If you were in the 22 percent bracket you would be looking at roughly $2,146 (22 percent income tax and about 15 percent SE tax).