It would help to know whether this is fertilizer for plants in pots or in the ground and maybe also what you are growing. Plants need many more essential nutrients than the calcium and potassium in egg shells. If you're growing in pots you have to supply them all, one way or another. If the plants are in the ground, most of the nutrients are there already although not necessarily in optimum amounts. If you're in an area where the soil pH is high due to calcium (which I believe applies to some areas of Texas), then plants in the ground won't benefit from egg shells.
There are a number of home-made fertilizer "recipes" on the internet. They won't necessarily be appropriately balanced and I have a suspicion that collecting together all the ingredients would often end up costing more than just buying some Miracle Gro at less than $10 for a 5lb bag of 24-8-16. Because they are made of household ingredients doesn't necessarily make them "organic" either.
Most commercial all-purpose fertilizers won't include calcium, and often not magnesium, but whether you need to supply those or not depends on the individual situation, it isn't one-size-fits all.
If you're looking to just supply calcium and magnesium, then sufficient egg shells and some Epsom salts might be what you're thinking of? Otherwise, if you're looking to supply everything a plant needs, you'd need more than one extra ingredient unless it's a commercial fertilizer that includes all the other essential nutrients.
