How accurate is YTD (12/31/18 paycheck) and my annual base salary?

I looked at my 12/31/18 pay stub and found that there is a $2500 difference between my YTD and my annual base salary. I don't know if this is normal, I honestly never looked before and I only looked now because I am going for a mortgage and they want salary proof and the amount I told them and that is in my offer letter didn't match my YTD. So, for example, my agreed upon annual base salary is 67500.00 and my YTD is 65000.16, I get paid semi-monthly.

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