To always know where you stand calorically you can choose one or two ingredients that you know the measurements to get consistency.

We researched the caloric values of ingredients in a Cosmo Recipe
and this is what we learned:

Calories in Vodka

The vodka you choose and the amount you use is the first consideration.

80 Proof Vodka has
                    96 calories, 0.0g of fat, and 0.0g of carbs per 1 ½ fl oz serving.
86 Proof Vodka has
                    105 calories, 0.0g of fat, and 0.0g of carbs per 1 ½ fl oz serving.
90 Proof Vodka (45% alc.) has
                    109 calories, 0.0g of fat, and 0.0g of carbs per 1 ½ fl oz serving.
100 Proof Vodka has
                    123 calories, 0.0g of fat, and 0.0g of carbs per 1 ½ fl oz serving.

Calories in the liqueurs used in a Cosmo Recipe

60 Proof Triple Sec has
                    36 calories, 0.0g of fat, and 3.2g of carbs per ½ fl oz serving.
Cointreau® brand liqueur (80 Proof, 40% alcohol)
                    47 calories, 0.0g of fat, and 3.7g of carbs per ½ fl oz serving
Grand Marnier’s brand liqueurs (80 Proof, 40% alcohol)
                    38 calories, 0.0g of fat, and 3.2g of carbs per ½ fl oz serving

The mixers used in a Cosmo Recipe

Cranberry Juice has
                    18 calories, 0.0g of fat, and 4.6g of carbs per 1 fl oz serving
Lime Juice has
                      8 calories, 0.0g of fat, and 2.8g of carbs per 1 fl oz serving

The garnishes used in a Cosmo Recipe

Lime slice has
                    3 calories, 0.0g of fat, per 1/8 slice
Lemon twist has
                    0 calories, 0.0g of fat, and 0g of carbs
Orange twist has approximates 3 calories flaming the zest all you get is the oils

Depending on the choices for ingredients you make the calories in your Cosmo can be as few as 72 or over 300. And the size of the glass and portions truly matters!