Actuarial notation includes features not currently supported by the existing <math> markup. The most important missing feature is the enclosing angle used to denote a duration in years. For details (including examples and current unsatisfactory workarounds) see:
https://en.wikipedia.org/wiki/User:Stelio/Actuarial/Notation

One solution is to include the actuarialsymbol TeX extension which provides this and other related functionality:
https://ctan.org/pkg/actuarialsymbol/

It would be fine if the required outcome is to use separate tags for actuarial notation on Mediawiki. Just as there is currently <math chem>...</math> (aka <chem>...</chem>), the actuarial notation could also be kept distinct by implementing <math act>...</math> (aka <act>...</act>) if needs be.

Thanks,
Stelio.