I am on a fixed income of 2500 a month and the total number of allowance I am claiming is 8 please tell me what is my take home monthly.
You should add a location to your post and more information. I am going to assume you are in USA. State income tax withholding varies between states, though, so I leave that to you. It also depends on if you are filing single/head of household/ married filed singly/ or married filed jointly. I'll assume you are single.
My best guess, given the lack of information in the question, is $2308.
Each allowance you claim reduces the amount of your monthly pay that is taxed by $329.20. Since you have 8 allowances, none of your income is subject to federal income tax. However, Medicare and social security both have to come out(assuming you are taxed for those programs). Social security is 6.2% which comes out to $155 a month and Medicare is 1.45% which comes out to $36.25 a month.
You can read up more about income tax and allowances at IRS Publication 15