Repayments on an Interest only mortgage.

demoivre

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350k at 4.69% nominal, 4.26% APR - what are the monthly repayments interest only? I say 350000(.04260/12) which equals 1242.5 per month ie the APR is used in the calculation: one of my friends ( who is taking out the loan) says 350000(.04690/12) which equals 1367.92 per month ie the higher nominal rate is usd in the calculation. Who is correct?
 
Thanks , I 've just lost a tenner :mad: but I can live with that! I based my calculations on my on experience of some interest only stuff that I have and in my cases the repayments are definitely based on the APR - I assumed that this was the case generally. It seems ponitless quoting the true rate ie the APR if nominal rates are used in the calculations. I have argued in the past on here that the amount repayable per thousand is a better measure of the cost of funds - this reinforces that view. Anyone got a loan of a tenner :D
 
Does this methodology apply to interest only, or is it common to all mortgages?
 
AFAIA minor differences can happen, where legal fees etc are included in the loan, and how the interest is calculated on the mortgage (most now apply interest on a daily basis).
Where a loan is discounted in the first few years of a mortgage you may get discount rate 3.5% nornal variable rate 4.5% APR 4.7% the APR being the actual interest rate spread over the full term of the mortgage.
 
This throws the cat amongst the pigeons imo if some banks are using apr's and some are using nominals to work out repayments - how are we supposed to make a valid comparison? IFSRA and the like insist on an APR being quoted but clearly it is of decidedly limited use as I shouldn't have been using it at all in the example of my mates borrowings! I would suggest again that the cost per thousand is what we should all be looking at.
 
CCOVICH said:
Does this methodology apply to interest only, or is it common to all mortgages?

It's pie in the sky stuff imo. A few years ago I asked IFSRA to point me to the formula that shows the relationship between APR and cost per thousand - they couldn't and you won't find it on the web either - there is any amount of stuff available if you Google APR but none will show the crucial link between APR and cost per thousand. This is very significant because if there isn't a commonly used formula to link APR and cost per thousand then none of us knows the implications for our repayments of say a 25 bp rates rise - we are at the mercy of the bank to tell us what the new repayments are. With an interest only mortgage it should be easy to work out the changes but now it seems that you need to know whether the bank is using APR or nominal! For my interest only loans the APR is used - I have just checked them again to make sure I haven't lost the plot!
 
I find using the financial function PMT in Excel very handy and accurate.
Don't know the basis of the calculations though

You can check this out by setting up a calculation every month for the term of the mortgage (little tedious)
 
Interesting thread about APR calculation at http://www.askaboutmoney.com/showthread.php?t=5012
for those interested. Extract below

The APR concept is relatively simple. Start with the basics: an APR of 10% means if I borrow £100, I repay exactly £110 exactly one year later. Thats why they call it ANNUAL PERCENTAGE RATE!

Now lets look at rates over other periods. Suppose I have a £100 overdraft at the start of year at an APR of 10%. In theory, if I make no other transactions on the a/c (inc fees charges etc.) I should owe exactly £110 at years end. How is this done if interest is charged, say, quarterly? Well, its not simply a question of paying 2.5% interest per quarter. Why? Because in quarter 2 I'd end up paying interest on £100 + £2.50 (total interest for the quarter being £2.5625, in quarter 3 I pay interest on £100 +£2.5625 + £2.50 etc.

To get the true quarterly rate I must convert the interest rate to the format 1+i where i is the decimal equivalent of the APR. In this case APR =10% = 0.1 so my 1+i format = 1.1 (which is the number I must multiply the year start debt by to get the year end debt.) Then get the fourth root of 1.1 (or the square root of the square root of 1.1) to get the 1+i factor for one fourth of a year. This is 1.024113589.... Therefore the true interest rate per quarter is 2.4113689%

You can check this as follows:
Quarter Opening balance Interest Closing Balance
1 100 2.411359 102.411359
2 102.411359 2.469505 104.880864
3 104.880864 2.529054 107.409918
4 107.409918 2.590039 109.999957

Correct apart from rounding errors; all figures shown to 6 decimal places.


Similarly the true daily rate is (the 365th root of 1+i) -1
In this case this is (the 365th root of 1.1) - 1
= 1.000261158 - 1
= .000261158
= .0261158% per day.

The Excel formula for 365th root of 1.1 is =1.1^(1/365)


Lesson 2 is how to calculate the APR when you know the repayments. Thats for honours students!
 
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