I have created a table of repayment schedule of a loan amount \$20,000 at 12% annual interest rate and a repayment of \$500 each month using Excel. The balance, using the first month as an example, is calculated as:
($20,000 - $500)*(1+12%/12)=$19,695.
| Month | Payment | Balance |
|---|---|---|
| 1 | 500 | 19,695.00 |
| 2 | 500 | 19,386.95 |
| 3 | 500 | 19,075.82 |
| 4 | 500 | 18,761.58 |
| 5 | 500 | 18,444.19 |
| 6 | 500 | 18,123.64 |
| 7 | 500 | 17,799.87 |
| 8 | 500 | 17,472.87 |
| 9 | 500 | 17,142.60 |
| 10 | 500 | 16,809.03 |
| 11 | 500 | 16,472.12 |
| 12 | 500 | 16,131.84 |
| 13 | 500 | 15,788.15 |
| 14 | 500 | 15,441.04 |
| 15 | 500 | 15,090.45 |
| 16 | 500 | 14,736.35 |
| 17 | 500 | 14,378.71 |
| 18 | 500 | 14,017.50 |
| 19 | 500 | 13,652.68 |
| 20 | 500 | 13,284.20 |
| 21 | 500 | 12,912.05 |
| 22 | 500 | 12,536.17 |
| 23 | 500 | 12,156.53 |
| 24 | 500 | 11,773.09 |
Although I can always update the table in Excel, but I wonder if there are formulas to quickly find out:
Given load amount \$20,000, monthly repayment \$500 and the remaining balance \$11,773.09 after the 24th repayment, can you find out the annual interest rate?
Given load amount \$20,000, annual interest rate 12% and the remaining balance \$11,773.09 after the 24th repayment, can you find out the monthly repayment amount?
Edited: I can answer 2. myself:
Monthly repayment amount = ($20,000*(1+12%/12)^24-$11,773.09)*(12%/12)/(1+12%/12)/((1+12%/12)^24-1)
I hope you don't mind if I answer indirecly instead of just presenting a result.
For machines running under Windows (what includes VM thereof), there is an "emulator" of the HP12C for download, the corresponding manual you may find here (Appendix D, Formulas Used, shows all used formulas). This virtual calculator offers an acknowledged standard of TVM (time-value of money) what enables you to answer your question in quite short time on your own. HTH