I’m a CPA, Deloitte Tax alum, and I personally prepare 150+ DE C Corp tax returns a year.
You will need to file your DE C Corp tax return by 3/15 every year. You can also go on federal extension to 9/15. State extensions vary. If you’re running at a loss, its better to go on extension so that you have more time to review the previous year’s financials. I’ve seen plenty of startups rush to get their taxes in by 3/15, only to discover a few months later that they need to add in a few expense reimbursements for the founders. Then we have to do an amended return.
Measure twice, cut once!
***Also note that DE C Corps have to file the DE Annual Fee by 2/28 every year. This is a calc driven off of your cap table and assets, and is typically between $400-$4000 for a seed / Series A startup.