Please visit the IRS site and use the withholding calculator -- it is the best way to know if you are having sufficient taxes withheld ---> https://www.irs.gov/individuals/irs-withholding-calculator
For a single person, not paying a home mortgage / property taxes, it would be dangerous to use a 8 allowances -- you are lilley to be quite a bit under-withheld resulting in interest and penalty charges.
