- At the end of March 2021, the P/E ratio to suddenly dropped from 40+ to around 25.
-At the end of September 2021, the P/E ratio suddenly dropped from 15+ to less than 7.
As far as I can tell, there was no abrupt change in the stock price
over the past year:
So if P/E made a big move, but the price (p) didn't make a big move; that means that earnings (E) made a big move.
For example if price is $100 and earnings is $2.5 then P/E is 40. But if the earnings go to $4 but the price doesn't change the P/E drops to 25.
In reality there was a change in both P and E which resulted in the P/E moving from 40 to 25.
from the website you linked to:
The price to earnings ratio is calculated by taking the current stock
price and dividing it by the most recent trailing twelve-month
earnings per share (EPS) number. The data is updated every 20 minutes
during market hours.
you should expect jumps when Price is updated every 20 mintes, but Earnings updated every 3 months.
The clue was that the jumps occur quarterly.