I read online that any amount of tuition assistance over $5250 is taxable. I am trying to figure out the amount I was taxed since I had to pay my employer back. If tuition was $20k, the taxable amount would be 20k - 5250 = 14,750. Question is if I live in California, what tax rate would I multiply by to get the amount I paid in taxes?
If $14,750 was added to your W-2 wages for Tuition Assistance, the tax rate you paid on that income would be your regular income tax rate.
TurboTax will tell you what your Effective Tax Rate is if you look at the PDF copy of your return, or, divide your total tax owed (line 16) on Form 1040 by your total taxable income (line 15).
For California, click this link for Tax Tables.
However, if you received the W-2 income in a prior year, you may want to go back into that return (save a copy first) and edit your W-2 income to exclude the amount of tuition assistance you received, to see the amount of tax you paid.
Here's detailed info (with screenshots) on Claim of Right Repayment Credit.