The numbers are close to 2014 - you just happened to use the Single (or Marred Filing Separate) tax table column to find $46,550, but then you added the joint standard deduction. Because the $46,550 was for Single, you'd add $6200+$3950 to get that min income. For Married Filing Joint you'd need $56,100 in taxable income to generate $7500 in taxes (from the tax table), so then you add $12400+2*$3950 assuming you're both not dependents.