Can you retire and start your ssa and than apply for ssdi

how accurate is the amount that is shown on my online account for ssa so in other words when i put in my dates for retirement [ie] age 63 or age 65 it will give me $ amounts is it very accurate or is it just an estimate if so when or how do I get exact amounts thanks for the help. The more I look in to retirement the more complicated it seems to be getting 🇺🇸✌️