It takes a ridiculous discount rate to effectively become 0 in 20 years. 5%/year * 20 years = (1-.05)^20 = 35.8%. 10%/year * 20 years = (1-.1)^20 = 12.6%. Sti

It takes a ridiculous discount rate to effectively become 0 in 20 years. 5%/year * 20 years = (1-.05)^20 = 35.8%. 10%/year * 20 years = (1-.1)^20 = 12.6%. Still, 100 years is often considered a reasonable limit on such things as 5% * 100 years = 0.6%.