Homemade sponge cakes last around 2 to 4 days as long as you keep the homemade sponge cake refrigerated.
After 2 days the homemade sponge cake will not be as fresh so it's best to eat the homemade sponge cake before 2 days for the best taste.
The homemade sponge cake gets stale after 3 days or so even when kept refrigerated so it's best to eat it within a few days.
If you have a store bought sponge cake those usually last around 5 to 7 days because those store bought sponge cakes usually contain ingredients that help to preserve the sponge cakes.
But homemade sponge cakes do not contain those preservatives so they don't last as long.
A homemade sponge cake or store bought sponge cake will usually be okay even out on the counter or in the pantry for at least a few days.