Is Zakat obligatory on money that has reached the Nisab, with an increase that does not amount to the Nisab?

If wealth reaches the nisab (definition) (minimum taxable amount) and a year has passed over it, zakat (definition) becomes obligatory on its entire amount at a rate of 2.5%. Anything in excess of the nisab is calculated at the same rate, as stated in the hadith (definition) of the Prophet, peace be upon him: "And there is nothing due on you—meaning on gold—until you possess twenty dinars. If you possess twenty dinars and a year has passed over them, then on them is half a dinar. Whatever exceeds that, then it is calculated proportionally."