Assalamu’alaikum Warahmatullahi Wabarakatuh
The money which is saved in the bank has similar law as saving gold. They are equally obligatory and should be paid as zakat if its nisab and its haul has been fulfilled.
Gold’s nisab is 85 grams to be paid as zakat. If it has been owned for one haul, or for 12 months qamariyah (Hijriyah) and the number after the year still 85 grams or more, so zakat that should be paid is 2.5 of the total value of gold.
Counting haul is done after a year since the amount of gold reached a value of 85 grams. For example, on the 1st of Ramadhan 1429 H, the amount of gold that you deposit is up to 85 grams, if on 1st Ramadan 1430 H, the amount of gold that you deposit into 100 grams, so you have to spend zakat of 2.5% x 100 g = 2, 5 grams of gold.
It is similar as your savings in the bank. Before reach the haul (one year) with an equally value as 85 grams of gold, there is no obligation to pay zakat.
Counting haul for savings is done after a year since the amount of money reached an equally value as 85 grams of gold. If the current price of gold is Rp 120.000 each gram, so when you reach Rp 120.000 x 85 grams = Rp 10.200.000,-, then started counting the year for nisab.
For example, the amount of your savings on the 1st of Ramadan 1429 H, exactly reach that number, and if your savings on the 1st of Ramadan 1430 H, your amount of savings is 20 million, at that moment, the Zakat that should be paid is 2.5% x 20 million = Rp 500,000. (Ahmad Sarwat, Lc/rumahfiqih.com)