Bouleversee wrote:So one loses 0.5% if one's certs. matured or had their anniversary in Jan. rather than Feb? I only had 2.2% RPI added in each case.
The month of the anniversary can make a difference. If you refer to this month's bulletin
https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/consumerpriceinflation/january2020/pdf
and search for 290.6 (Jan 2020 RPI figure) which occurs first on page 12, you will note that 12-month figures for RPI inflation for Jan is 2.7%, but for Dec is 2.2%. So there can be a difference between a certificate that has its anniversary one month, and the same certificate that has its anniversary the following month.
Also note that (as pointed out in PinkDalek's response) that NS&I use the RPI/CPI figures from 2 months previous ("lagged" in the statistical jargon) to do with publication and computations times. So if you have a certificate with an anniversary in Feb, the relevant RPI/CPI figures are from Dec.