Husband retired last yer. Should I change codes on W4 to C spouse not working or leave on D? We still paid taxes the last 2 years because he gets pension and SS. I work.

I can't find any info on how the letters C for spouse not working or D both working  change your tax amount taken from check. My husband isn't working but does get close to what he made before with both checks. He's 68.  Thanks