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.
A trust created during the lifetime of the person who created the trust. If irrevocable, income on the trust principal is generally shifted to the trust beneficiaries.