Calculating NS Index linked saving certificate values

Stompa

Lansdowne wrote: »

...you may have a point that the values do not move to the next RPI value on the first of the month, but on the "monthiversary" as someone called it.

If you look at the 5 year lookup tables in NS&I's own spreadsheet, then up to about a year ago the values always changed on the first of the month. Since then though it's been a bit more variable. It also changes on the following dates:

29 Apr 2009
12 May 2011
07 Sep 2011
20 Sep 2012
30 Sep 2012
15 Oct 2012
29 Oct 2012
13 Nov 2012
27 Nov 2012
12 Dec 2012
27 Dec 2012
10 Jan 2013
25 Jan 2013
08 Feb 2013
23 Feb 2013
27 Feb 2013
19 Mar 2013
13 Apr 2013
07 May 2013
31 May 2013
25 Jun 2013
05 Jul 2013
19 Jul 2013
30 Sep 2013
12 Dec 2013
23 Feb 2014

I've no idea why! Perhaps there's a good reason for it, but it's difficult to tell since we're unable to see the inner workings of the spreadsheet.

talexuser

Lansdowne wrote: »

Talexuser, that link is to the ONS, not to NS&I. The ONS (Office of National Statistics) publishes the index values, but is not in any way responsible for the calculations of NS&I certificate values.

Ok, thanks, a pity

Got the same reply from them again as some days ago

"Thank you for your enquiry,

I am sorry you have had to contact us with regards to this issue.

I can confirm we are currently experiencing problems with the online calculator and this is being investigated.

Please allow a few more days for this to be resolved and try again later in the week.

Kind Regards

Julie Griffiths
Customer Service Team
NS&I Blackpool"

Not a great deal of help, the longer it carries on.

cepheus

talexuser wrote: »

Last week I sent a message on the contact page asking why the totals were moving around, no reply yet.

Maybe if all of us did the same it would hurry things up a bit? Even ask for their formulas - there is a link to their statistician.

http://www.ons.gov.uk/ons/rel/cpi/consumer-price-indices/january-2014/stb---consumer-price-indices---january-2014.html#tab-statistical-contacts


I know it's kind of funny at the moment, but this is OUR interest we are talking about and we need have some confidence they know what they are doing here.

reply here

The basic principle of indexation is to take the index values at the start and end of the period in question and calculate a percentage difference between the two. I would be happy to talk you through the steps you need to take on the phone if you would like? However, you will need to contact NS&I for the exact details of the calculation that they undertake as this is an issue for them, not ONS.

seems that it was waste of time writing!

cepheus

talexuser wrote: »

So is it as easy as noting the index in the month you start, the index in the month you end (say after 5 years), subtract and add the 0.5% to get the interest?

No or else it would be easy.

It's usually two months before the start and two months before the anniversary (I think), but I suspect which month to use depends on the exact date you took it out and the certificate, as detailed in an earlier post. Also some certificates don't have a fixed % to add but gradually increase every year to average the stated % over the term. This procedure gets five out of six out of my certificates to within about £10 out of a 15k to 20k investment (some are rolled over). There are also some other rules such as ignoring negative annual changes in RPI.

The other one is around £400 out, I suspect NS&I have it wrong.

talexuser

So is it as easy as noting the % difference between the index in the month you start compared to the index in the month you end (say after 5 years), add the 0.5% to get the interest?

talexuser

Calculator has changed since yesterday. My 5 year from May 2011 is now showing a 11.15% increase.