The normal way to pay off a loan, called an amortization, is to pay the a fixed amount each month, as in your case. The amount consists of two parts, the interest on the outstanding loan since the last payment (one month's interest), plus a certain amount that reduces the outstanding debt.
In your case, you borrowed $25,000 on N0v 1, 2003, and you are to pay them $268 each month for the next 10 years. In a normal amortisation plan, I calculate the monthly payment as $277.56, so, I don't know how your figure of $268 was arrived at.
In any case, you will have to calculate what you owe your parents as of the current day, by figuring out that you were going to pay them $268/month, of which, for the first month, 6%*25,000/12 = $125 would have been interest, and the remaining 268-125=$143 would have been payment on your debt, leaving 25,000-143=$24,857 as the debt at the beginning of the second month. You would recalculate the interest on that debt at the end of the month, subtract the interest from the debt, and that would be the new payment on the debt, etc., etc. Any overpayment, say $1000, instead of $268, you would simply calculate the interest due for the month(s) since your last payment, subtract that interest payment from the $1000 payment, and deduct that remainder from the debt. Etc. But, you have to know each date of payment. Failing that, you will just have to guess as to the actual payment dates, check with your parents and, if they agree, go with that.
Now, all the above can easily be programmed into an Excel spreadsheet, using formulas and some common sense.
If you have a problem doing this, send me a PM with your email address and all the data that you can, and I will communicate with you in by email, so that I can then attach a spreadsheet that does this for you.
