Muffins and cupcakes are made in the same type of pan, in the same shape, using much of the same ingredients. So, does it just come down to sugar content? It turns out the contrast lies in a few things: flavors, texture, method of preparation, and (yes) a bit of sugar.
Cupcake vs Muffin Which one do you prefer? Since today is National
Difference between cupcakes and muffins
10 Tips to Bake Perfect Cupcakes - Life As A Strawberry
Vanilla Cupcakes (that actually stay moist)
How to Make Muffins (Plus Pro Tips & Recipes) - The Busy Baker
Muffin and Cupcake Pans 101, Wilton's Baking Blog
Muffins vs Cupcakes - Cupcake Project
Cupcakes vs Muffins
NO MORE CONFUSION! True Differences Between Cupcakes and Muffins
5 Steps to Convert a Cake Recipe into Cupcakes
Cupcakes and Muffins: Same Or Different? Know Here