If the ED acceptance rate is 50%, then maybe you can assume a 60% chance. If the ED acceptance rate is 20%, you can make no such assumptions.
Keep in mind that the ED acceptance rate is typically higher than the RD rate. However,at some colleges, if you back out athletic recruits, major donors’ kids,and other heavily hooked kids, the difference id less statistically significant.
At the end of the day though, guessing an acceptance rate to a selective school for an individual without a complete application in front of you is a parlor game at best.