I Tested Boxed Cake Mix Without the Eggs, and It Was Fantastic
Boxed cake mix is un-ruinable. Trust me, I've tried.

There was a time, not so long ago, that I was completely abusing my right to use boxed mixes. I made a crumb cake out of muffin mix, peach dump cake, very convincing black and white cookies, and a super tender boxed cake by adding too much oil and not enough egg. I’ve learned a lot from all this screwing around with boxed mixes (for science, of course). With the recent surge in egg prices and the rate of birthday celebrating as consistent as ever, I began to wonder if there was a way for folks to make boxed cakes without using up all of their precious eggs. Then I remembered, of course there is—you can skip them completely.
It was when I was trying to manipulate boxed cake mix to make thick, soft black and white cookies that I made this crucial discovery: All boxed cake mix wants to be cake. I used Duncan Hines yellow cake mix and tried everything to change the batter. I took out the oil. I added only egg. I added just a few tablespoons of water. All of my attempts bubbled, spread, and puffed into full-blown cake. I ended up using muffin mix to come up with the right consistency for black and white cookies.
If you think about it, this basic understanding (that cake mix will always become cake) is why we know dump cake works. For those unfamiliar with this casually named dessert, you simply dump fruit (canned or otherwise) into a casserole dish and sprinkle dry cake mix over the top. Even the scant liquid from simmering fruit is enough to moisten the dry cake mix and activate it. Boxed cake mixes, like those from Duncan Hines, Pillsbury, or Betty Crocker, are all designed to be nearly foolproof. You just need to add liquid—eggy or not—and it will become cake.
Don’t get me wrong, in a side-by-side comparison (see one below) you’ll notice the difference in puff and color, but the flavor is consistently good. It’s really hard to screw them up to the point that they’re not delicious. I’ve been trying for years and I haven’t managed to make it taste bad. Changing the ratios, especially the oil, might actually give you a cake texture you prefer (more on that later).
Two, one, or zero eggs all result in cake
I wanted to test out how far I could push cake mix so I did a Funfetti test. The batter, prepared with the manufacturer’s suggestions, takes a cup of water, half a cup of oil, and three eggs. I did a few iterations. One test with only a single egg and double the oil, one test with no eggs and double the oil, and one with the proper amount of oil but zero eggs.

While the mixture properly prepared according to the package’s directions has more of a domed top than the other reduced-egg versions, absolutely all of them became fluffy, soft, delectable cake layers. I think the single egg and double oil cake was my favorite because the single egg was just enough of an emulsifier to support the extra fat. It wasn’t weighed down, but it was decadent and moist.

But I digress: The real victory here is that the cake with absolutely no egg was fantastic. It didn’t dome, which is actually preferable if you’re stacking layers for a cake with icing, the texture was fluffy and moist, and the flavor was as Funfetti as could be. There was no need to replace the egg with anything, by the way. No extra water. No banana. Just mix the indicated amounts of water and oil into the dry mix. Pour it into the pans and smooth out the tops. Keep in mind that you can do anything in between too. Add one egg. Maybe you have two leftover egg whites. A stray yolk lurking in your fridge? Toss it in instead of the suggested three whole eggs.
Not all boxed mixes are as forgiving
While boxed cake mix is completely fine without eggs, not all boxed mixes are as forgiving. I tried to skip the egg in boxed Ghirardelli walnut brownie mix and—ho boy. That was absolutely disgusting. I was surprised, honestly; I figured since there was only a single egg in the recipe, what harm could it do to skip it? Lots. I made six brownie bites—three with a no-egg mixture, and three with the batter prepared according to the manufacturer’s directions. You get three guesses which is which.

Eggs are an emulsifier after all, and it seems like brownie mix truly needs the help of that single egg to integrate the fats and yield a moist and ungreasy final product. Your brownie mix is not the place to skip eggs. Do that with boxed cake mix instead.