my normal tax is R3600
13th cheque tax is R6300
0 – 165 600 18% of each R1
165 601 – 258 750 R29 808 + 25% of the amount above R165 600
258 751 – 358 110 R53 096 + 30% of the amount above R258 750
358 111 – 500 940 R82 904 + 35% of the amount above R358 110
500 941 – 638 600 R132 894 + 38% of the amount above R500 940
638 601 and above R185 205 + 40% of the amount above R638 600
See the effective tax rate on R20,000.00 a month is 15.14 % because of the sliding scale (R 240,000.00 a year)
However when you receive your "13th cheque" you pay the highest tax bracket that you TOTAL annual wage will fall into (if a part of the 13th cheque pushes you into a higher tax bracket for total annual income just calculate it with fractions). If you are earning R20,000 a month, you earn R240k a year thus putting you in the "25%" tax bracket for you 13th cheque (up to R18,750, after whjich you fall into the next tax bracket for the fraction of the 13th cheque that puts your total income over 258,750).