Deducting an amount from income and getting a refund are two very different things. Your interest will reduce your income, not give you a dollar for dollar refund.
You don't always get everything back. Filling out
a tax return is a process of reconciliation for a particular year. All of your
income is taken into account with all your deductions and personal
exemption and possible credits. Next, you arrive at your taxable income. The
withholding is used to pay tax on that income. If there is anything left over,
you get it in the form of a refund.
The more
income you have, the higher the tax bracket you may find yourself in. The
higher the bracket, the bigger percentage of your income is taxed. Here are the
brackets for 2017:
https://taxfoundation.org/2017-tax-brackets
