Is zakat applicable on money kept over a year or on recently acquired money?

The easiest way to calculate Zakat is to have a fixed day every year. So, for example, the first of Ramadan or whenever it is that you've gone over the Nisab for the last 12 months. And then, you know, in this example, the first of Ramadan, what I need to do is go online, check my bank account, check any cash that I have, the value of any gold or silver and so on, and then work out that total and do 2.5% of that amount. That's all you need to do. That's the safest and easiest way and the way, inshallah, to make sure that nothing is missed out.