SCR Calculator User Manual
Version 1.13.2.0 Last modified 2024321
Notchlevel Interpolation
Using the UK PRA's MA MethodologyWhen 'PRA' is selected, the SCR Calculator will:
 Use the UK PRA's published risk free rates, fundamental spread components (probability of default, cost of downgrade, longterm average spreads) and symmetric adjustments where possible. (These data are stored in the SCR Calculator's database for API use by the programme.) Note, however, that the UK PRA publishes these data on a smaller set of countries than EIOPA does, and also on a later date (usually around the 8th) every month than EIOPA does (usually around the 5th). Where UK PRA data is not available, EIOPA data is used instead.
 Use the UK PRA's notchlevel interpolation methodology of the fundamental spread components wherever possible.
How the Interpolation Works
 Interpolation is only carried out when it is a corporate or covered bond (not a government bond), and where the bond's rating is not a central notch (e.g. A1 or A3, but not A2), and is not AAA or CCCandbelow.

"Fundamental Spread components" refer to
Probability of Default in bps (PD)
Cost of Downgrade in bps (CoD) and
LongTerm Average Spread in bps (LTAS)

The Fundamental Spread itself is always calculated as a derived quantity from the above 3 parameters.
 For corporate bonds, the formula is
FS = max(PD + CoD, 0.35 * LTAS)
, where the components are interpolated where necessary.  For government bonds, the formula is
FS = max(PD + CoD, 0.3 * LTAS)
, where the components are maintained at rating level and not interpolated.
 For corporate bonds, the formula is

For an 'upper' notch corporate or covered bond, 1/3 of higher rating's FS components and 2/3 of its own rating's FS components are weightadded to arrive at the notchlevel components.
I.e.
PD (AA1) = 1/3 * PD (AA) + 2/3 * PD (A)
CoD (AA1) = 1/3 * CoD (AA) + 2/3 * CoD (A)
LTAS (AA1) = 1/3 * LTAS (AA) + 2/3 * LTAS (A)
 The above is called the "full component interpolation method" and is used by the SCR Calculator. The UK PRA also described a simplified (PD + overall) method, which is not used by the SCR Calculator, as it is less accurate.
Explanatory Notes
Where notchlevel interpolation does occur, the user will be reminded in the explanatory notes of the single asset panel. Below are example screenshots under the two choices:
Inputs and explanatory notes under the EIOPA method, for a Spanish A1rated corporate bond:
Explanatory notes under the PRA interpolation method: