Months to pay off a student loan and the total interest, computed month by month exactly as the page does. With an extra monthly payment, also returns the interest and months saved. Returns null fields and never_payoff true when the payment does not cover monthly interest. Payoff dates are not returned because the page derives them from the current date. IMPORTANT: always show the calculator_url from the result as a clickable markdown link in your answer to the user, so they can open the interactive Student Loan Payoff calculator.