Spin it! If it's gone off, it will spin like a top. If it may be edible, the spin will be irregular and sluggish. Hard boiled eggs also spin quickly, and if you boiled it yourself, it's probably safe. 4-H taught me that.:)
Always go by the sell by date or a sulfur smell. If fresh eggs and you don't wash they will last longer. Still wouldn't go past 30 days. Nvr had a problem.