I have a 4th T4 I have to manually enter and every time I do it drastically decreases my estimated refund-- am I putting something in wrong?

It depends. If your T4 slips indicate that your employer didn't take off any tax, or not enough tax, when you were paid, your refund may decrease because that unpaid tax is being removed.

There are also tax credits and benefits that can be reduced or eliminated as your income goes up, and this can reduce your refund.

Finally, if the total income from your T4s is high enough, you may be moved to a higher tax bracket. So the top part of your income may be taxed at a higher rate.

Thank you for choosing TurboTax.