Trying to determine my due date.

The date of start of my LMP was 12/28/15. The length of my cycle averages at 34 days (kinda long!). The only time I had sex after 12/28/15 was 1/21/16.

Because my cycle is long, I keep getting different results when I go to a pregnancy calculator online. My first ultrasound and appointment is this Wednesday, so I know I'll have a better idea then. But I'd like to put my due date into some apps and sort of track how far along I am.

Is there a calculator that takes into account: date of LMP, cycle length, and estimated conception date?