Your interest rate includes the interest percentage you will be charged for taking a loan out, accrued on a daily basis, and does not include any other fees. An APR is defined as the sum of the interest rate plus extra fees and expressed as a percentage.
Since SoFi does not charge any fees, your APR will normally equal the interest rate, but there will be instances where your APR is different because of your first payment due date, which is determined from the time of disbursement.