Is Zakat obligatory on money saved in a savings account throughout past years, and what is the ruling on not having paid it for that period?

Whoever owns money or trade goods that reach the nisab (definition) (the value of 85 grams of gold) and a lunar year has passed over it, must pay zakat (definition) on it, which is a quarter of a tenth (2.5%). Zakat does not cease to be due with the passing of years; rather, it remains an obligation and must be paid.

You must pay the zakat for every year that has passed during which you owned the nisab and a year passed over it, and you did not pay the zakat, up until the date you bought the house. What you paid to your brothers and sisters does not count as zakat because there was no intention of it being zakat. Similarly, what you paid to your father is not considered zakat, because his maintenance is obligatory upon you if he is poor, and he is not eligible for zakat if he is rich.