Dieting by calories

Watching calories won't be enough if you're looking to keep this weight off. Losing weight and keeping it off is a lifestyle change, not a temporary diet. If you are looking to make the change, I'd suggest reading a great article called Lifestyle Changes, Not Diets, Are Key To Losing Weight that was published on Medical News Today. I think it really sums up the important aspects that most people need to change to successfully lose weight and keep it off. The three points I spend extra time focusing on are portion control, drinking lots of water and making exercise a part of my daily routine (even if it means taking the stairs instead of the elevator or parking my car further from the entrance of a store/restaurant).
I hope this helps.

Yes you can lose weight just by diet.  In fact diet is more important than exercise as long as you have an active lifestyle.  Do you take the twins for a walk - that's exercise.   Carry the laundry up and down steps - that's exercise.  Clean your bathroom - that's exercise.

Eat healthy, don't be a couch potato  and you will be fine.