I need help on what formula I can use to work out an APR for a loan where the pay back is loan plus full interest divided by equal number of payments over the period. So, If a loan is £1,000 say at a simple monthly interest rate of 3% over 12 months, the payments are £113.33 each month to cover the full year's interest plus principal, thus paying loan and interest back each month. How do I calculate an accurate APR?