The bad news is that Americans need to reach into their pockets today, the good news is that it's a seasonal low point for the month. according to this Goldman Sachs chart.

Tax day seasonals

All that said, the Israel-Iran fighting is going to be the dominant theme in trading today.

S&P 500 futures are up 0.4% while European stocks are widely higher (+0.4% to +1.0%) outside of the UK (-0.4%).