Questions about Zakat

Hi, Ramadan Mubarak, I have a question about Zakat. It's my understanding that Zakat is paid on the wealth you have held for 1 year. But how do you keep track of what you have had for 1 year? It seems impossible to me lol.

Also, if I just paid 2.5% of everything thing I had each year instead of tracking it, would that count as Zakat + extra? Or would it be invalid?

Thanks, apologies if I don't reply quickly.