<p>If your federal wages and medicare wages match on your W2 and you contributed to a 401k pre-tax, there is a problem with your W2. Your federal wages + your 401k contribution (up to the 2012 limit of $17,000 or 22,000 for catch-up) should add up to your medicare wages. Did you contribute to your 401k on an after-tax basis? That is the only reason I can think of that it wouldn’t be on your W2.</p>