How do I determine if RMD applies Single Life Annuity full cash refund where I receive monthly lifetime payments from it since retirement from company where I worked?

It depends. If the annuity is part of a tax-deferred retirement plan like a 401(k) or a traditional IRA, then RMD rules generally apply. However, if it’s an annuity purchased outside of a retirement account with after-tax dollars, RMDs typically wouldn’t be a factor and there is no RMD requirement.

If you aren't sure, you may wish to check with the administrator of your retirement plan.