Thank you both, this is what I suspected. What is frustrating is, I am not even changing employers, I am changing roles in the same parent company, but the roles report to different sub-companies or LPs. This is the third time in 4 years this has happened to me about half way into the year, causing me to grossly overpay social security tax. It always gets refunded, but I would of course prefer my taxes to come out even. But I guess there are worse problems to have. Good advice on adjusting the W4 number, I may look into that.
