I had success with a smartphone app (loseit) and estimating. You really don't need to be more precise. Lost 3-4 kilos in a month. Doing a rough calculation will

I had success with a smartphone app (loseit) and estimating. You really don't need to be more precise. Lost 3-4 kilos in a month. Doing a rough calculation will often do the trick, that one sandwich could be 400-500 calories, and you had two beers, which is already 400-500. A weight losing calculator suggested you can eat about 2000 calories that day. So that's already half o your daily intake. But if you go run or cycle for an hour you can eat maybe 300-400 more. Keeping track breaks the bad eating habits.