I retired in 2018 and my former employer sent a W2 this year showing a taxable benefit in boxes 12a - 12d with codes C, M & N for Group Life Insurance coverage over $50,000. C = 1,310.64, M = 81.26 and N = 19. From what I have been able to dig up I understand that M & N are owed as uncollected Social Security and Medicare taxes. It seems my refund was reduced dollar for dollar for M & N. But the reduction of my refund was around $300 for the entry in C (which I never found any documentation for owing taxes on that). If C is taxable, why would the tax rate be in the vicinity of 22.9% (300 / 1,310.64) when my top tax rate is still in the 12% range? Thanks.