Question about LES and taxes/social security/medicare

Hi

So I'm trying to calculate net pay of my future military paychecks and looking at my LES and whatnot. Something I have noticed is that it seems like my federal taxes, social security, and medicare deductions all appear to be a bit lower than what should be coming out based on my research. I can't figure out exactly the percentage of what should be taken out of my federal taxes because I don't understand the tax brackets and stuff that well, but from what I'm reading is that Medicare should take out 6.2% of my gross income and Social Security should take out 1.45%.

However when I calculate the numbers, Social Security is taking out about 5.4% Medicare is only taking about 1.25%. Additionally, Federal Taxes is taking out about 6.2%.

For clarity, I am an E-4 with 2 years of service so I'm not making that much to put it into perspective. Also I believe I am correctly factoring in the income that is taxable (My base pay and a special pay that I have confirmed is taxed). BAH and BAS is not taxed of course.

EDIT: Also since being in the military and doing taxes, I usually get like 5 dollars back each year so it seems like that stuff is being done mostly correct

My question is, why the discrepancy? Is there something I'm missing? I'm trying to calculate my net pay if I were to become an officer and if I can't figure out these calculations then with more income the difference is much larger.

Thank you in advance!