How do you calculate the power output of 238Pu over 25 years?

according to wikipedia:

“Most RTGs use 238Pu which decays with a half-life of 87.7 years, therefore diminish in power output by 1 − 0.51 / 87.7 or 0.787% of their capacity per year23 years after production, such an RTG will have decreased in power by 1 − 0.523 / 87.7 or 16.6%, i.e. providing 83.4% of its initial output. Thus, with a starting capacity of 470 W, after 23 years it would have a capacity of 0.834 * 470 W = 392 W.”

however, a more reliable source, states that the half life is 86.41 years….

how does one calculate the power output over 25 years?

i’m dying…