Nothing changed in my job/filing status, but my 2020 taxable income increased more than my wages and I don't think I'm in a higher tax bracket than in 2019.

Look at your 1040 and see where the additional amount is coming from. In addition, it is helpful to compare 2020 with 2019, line by line to see any irregularities.

To view your 1040 form, follow these steps: 

1. Sign in at TurboTax.com and select the blue Take Me to My Return button, if you haven't already done so.
2. On the welcome back screen, select Tax Tools from the menu on the left side of your screen (click or tap the 3 lines in the upper-left corner if you don't see this menu).
3. Select Tools, and then select View Tax Summary
4. Preview my 1040 under Tax Home (sidebar)
5. Click Back near the top of your screen to exit the preview screen.