I have heard that the salary for expats has been deducted the social securities before tax( Although I’m not so sure about that,the result may be approximate),so the calculation below doesn’t take them into consideration.
(Living allowance should be counted into monthly salary for tax calculation unless you are working for the government)
Your salary after tax deduction is as followed:
1.the tax monthly for the former 11 months:
(16400*1.25-4800)*25%-1005=2920
2.the tax for the last month(the 13th month salary be counted into Dec.):
(16400+16400*1.25-4800)*25%-1005=7020
3.your annual salary after tax deduction:
(16400*13+16400*0.25*12)-(2920*11+7020)=223260
so your monthly average salary after tax is 223260/12=18605 rmb
If you need convenience,you can surf http://www.baidu.com(百度）for（个人所得税计算器),if you want to know more,check out the attachment.