Mortgage interest differing pcm on a fixed rate - so boring!

[Interestquestion]

Can anyone answer a question I have about the monthly interest I pay each month on my fixed rate?

I have fixed at 1.39 until 2027 and have around £80k to pay off. I try to overpay when I can and am limited to £999 pcm without penalty.

Mortgage payment comes out on 1st of the month. Regular payment is £536.

what seems to happen is that i have my balance which I check and in this case it was £82,397 after an OP of £650 at the end of June.

On the 1st July the interest of £127 was added / applied. Usually it is £99 or £97, OP or not. Then the payment was taken of £536 as predicted.

can anyone explain why I would be paying £127 interest randomly one month? I have just under 15 years left to go and I don’t understand why the monthly interest amount is so inconsistent on a fixed rate? I made OPs with a view to paying less than £100 pcm in interest and I don’t understand what’s happening!

Is it different number of days in each month?

I don’t think so as it would be a much smaller fluctuation? (Wouldn’t it? Now I don’t know). June had 30 days which is less than usual so I don’t know why it would stuff on 25% more for a medium month. I can’t get my head round it at all.

Following with interest because this happens to to us aswell, every month the interest paid is a different amount, we are also on a fixed deal.

I’ve just gone back over my nerdy notes and this is what I paid in interest each month;
July 1st £127
June 1st £95.37
May 1st £99.07
April 1st £97.12
March 1st £102.05

my OPs vary and sometimes there are none, but the leap is big. I’ve googled a lot and can’t find any reason BUT if no one can help I’ll ring them (poor advisers) tomorrow and ask about it and report back. It’s driving my sad little money brain nuts.

Did you get an answer?

Could you enlighten us please 🙏

@Interestquestion I'd like to be able to enlighten you, but I can't, unfortunately. Did you phone them today?

Does your bank inform you of the interest calculation each month?

I just get an annual statement with the total years payments listed out and a total interest added amount.

I'm envious of your interest rate. I should have re fixed mine earlier & for longer!! I'm now on 2.48% for 5 years. I looked at 10 years, but the ERC was too high to risk. (I may have to sell & go overseas).

So I did ring them - it seems like it was most likely an issue with the online portal making an error and they said I’d actually been charged £97and they would send a transaction statement to show that I hadn’t paid extra. The woman on the end of the phone was so helpful and went through the most painful of detailed figures with me to try and help me work it out.

the way I work out the interest each month is:
my monthly payment goes out on the 1st of the month.

• I look at the figure of my outstanding mortgage balance before the 1st. For the sake of illustration, say it’s £82,500 on June 28th.


• Then on the 1st, they apply the interest, and the balance increases eg to £82,600 showing £100 in interest.


• On the 2nd (assuming these are all working days), they apply the monthly payment (eg £500) which brings the balance down to £82,100.

£82,500 - £82,100 shows the capital I’ve paid off is £400 and therefore the interest is £100.

or simply 1st of the month (July) figure minus end of the preceding month (June) will show it a day earlier.

it varies by a few pounds and pence each month, sometimes due to OPs. But this jump was surprising and they couldn’t work it out and all credit to her we spent a long and boring time trying but it’s being sent to the team who do the portal to try to see if anyone else has noticed the same thing.

every other interest payment I calculated exactly matched up to the penny with the numbers she had so I know I haven’t been making the wrong calculations regularly at least.

not sure if that helps anyone!

Oh, I'm glad it hasn't actually (against all sense) gone up for you.

yes your explanation made sense, I just wondered if they sent you/showed on line the interest calculation without you having to do what you do.

mine is always roughly where I expect it to be each year, so I'm not worried, but I might check tomorrow to see how much the interest is now each month and try to get it under a set amount I'll see how much I need to pay off to do that. You should have seen the calculations before I fixed it this time. I'm a numbers kind of person & I love using the various calculations to wirk out the impact of xyz.

Ha! Yes - I’ve just been working out how much more I need to overpay to get my monthly interest under £90 pcm as my next milestone.