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.
Shifting income to a later year, such as where you defer taxable interest to the following year by purchasing a T-bill or savings certificate maturing after the end of the current year. Investments in qualified retirement plans provide tax deferral.