You can always find a company that will let you call yourself whatever. At some companies they may call you senior and at some companies they may just call you

You can always find a company that will let you call yourself whatever. At some companies they may call you senior and at some companies they may just call you a software developer. But my guess is that you're asking about this because you're seeing job posts that say "senior developer". In that case I'd say just ignore "senior" and if you feel like you meet 50% (or something) of the important qualifications, apply. You never know what a company's pipeline looks like. It does you no harm to try.