Using the MORTGAGE2 PRO software, is easy to verify that $15,440 is the correct amount to be paid to the lender. One merely highlights the 24th payment of the amortization schedule and clicks on the renewal icon and fills in the renewal rate of 7% and the results are below;
If one was only interested in the IRD calculation without using the MORTGAGE2 PRO amortization software then you could use the DISCOUNTING.EXE program to arrive at the same numbers as shown below;
DETAILED ANALYSIS OF THE SEMI-ANNUAL COMPOUNDING IRD EXAMPLE
If Bob and Mary decide to pay the IRD, they could add the $15,440.04 directly onto the balance owing of $150,000 along with the 24th payment and thus the interest rate would be 7% from this point on until 36 payments have been made. From Figure 14 it can be seen that after 36 payments the balance owing is exactly the same (within a few pennies due to rounding off ) as it should be because that is what the IRD calculation is intended to achieve.
For this analysis it is assumed that the IRD money is borrowed. The IRD could be obtained from another investment but that would make the example more complex. Having the IRD money as a windfall (money under the mattress) makes the benefits obvious. If Bob and Mary decide to keep the two loans separate; then, the first loan is $150,000 @ 7% with $1,443.79 per month and the balance owing after 36 payments is $126,824.05
The second loan of $15,440.04 @ 7% with 476.04 per month (except for the last payment of 475.96) and the balance after 36 payments is zero.
An annuity calculation would show that 476.04 deposited every month at a monthly interest of .575% would accumulate to $18,980 after 36 months.
It can also be seen that a negative amortization schedule would give the same balance owing of $18,979.73 (close enough to 18,980). The approximate difference between $145,803 - $126,824 = $18,979. In other words, $15,440 now is worth $18,980 thirty six months in the future (FV) if it is appreciating at .575% per month . Stated differently, $15,440 now is worth $18,980 three years in the future(FV) if it is growing at an effective interest rate of 7.1224415.
Note that most interest rates are not normally quoted to more than two decimal places because of the difficulty in getting agreement in the PV/FV calculations as the equations exponent is very sensitive to the number of decimal places used!
Another way of looking at the numbers is as follows. If one deposits $476.04 per month, every month for 36 months, into an account paying interest at 0.575% per month then after 36 months $18,980 will have accumulated.
I = 0.575000
N = 36.0000
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