Need to know the exact date to switch futures expiration.

[Tylerweitz11]

Is there a reference source that I can use to determine the exact date when I should switch the monthly/quarterly expiration of the futures contracts I am trading? I believe this is based on the number of contracts being traded of the different expirations, but that is more of a hit-or-miss when the volume starts to shift.
I have an automated system for trading various Index and Commodity futures and I'd like to program this change so it is handled automatically.
Thanks in advance for any responses.

Here you go. Also, your broker should tell you when the expiration is about to happen. NinjaTrader (my platform of choice) does.

https://www.shadowtrader.net/futures-rollover-dates-futures-trading/