Your zakat payment period for the year will start on the date when your wealth first equalled or exceeded the nisab. After this, zakat must be calculated and paid once each lunar year has passed, and it will then fall every year thereafter on that date. If you are not able to remember this date, then you should make an estimate. If this is not possible, you should select a specific Islamic date to adhere to, instead. It is not obligatory to pay zakat during Ramadan, but many Muslims prefer to give charity during Ramadan.
