The IRS sets an interest rate each quarter that is applicable to underpayments by individuals. The rate for the third and fourth quarters of 2020 is 3%. You can see all interest rates listed by the National Association of Tax Professionals at https://bit.ly/3bVcCmw.
Items directly reducing income. Personal deductions such as for mortgage interest, state and local taxes, and charitable contributions are allowed only if deductions are itemized on Schedule A, but deductions such as for alimony, capital losses, moving expenses to a new job location, business losses, student loan interest, and IRA and Keogh deductions are deducted from gross income even if itemized deductions are not claimed.