Praise be to Allah.
If a person receives an amount of money that he could not have received before, like a bonus or lump sum paid at the end of a period of work, or on retirement, no zakat is due for the time that has passed. Zakat must be paid on whatever is left of that money after an entire Hijri year has passed.
If tax or anything else is deducted, then zakat is due only on the amount which the person receives, and after one year has passed.
And Allah knows best.