How is zakat calculated on saved money and earned money? Is it obligatory only on the annual increase? And what about the zakat of past years that I was unaware of?

Zakat is obligatory on invested capital if it reaches the nisab (minimum threshold) and a full lunar year (hawl) has passed on it, as well as on its profits. As for capital invested in a fixed asset that is not for sale (such as an apartment for rent), Zakat is only due on its income. If Zakat was not paid correctly in the past, it must be paid now. Zakat must be disbursed to the deserving categories mentioned in Surat At-Tawbah/60, and it is not permissible to spend it on building mosques, according to the majority of scholars. If you did so in the past based on a fatwa, then there is no blame on you; otherwise, the due Zakat must be paid. Debt does not waive Zakat, so Zakat is obligatory on owned wealth even if its owner is in debt, unless the money is spent to settle the debt before the hawl is due.