How many allowances should i claim im head of household with one child?

[Critter]

No one here can tell you that due to there being too many moving parts to get that answer ... 

Try these tools:

http://www.irs.gov/Individuals/IRS-Withholding-Calculator

 https://turbotax.intuit.com/tax-tools 

http://turbotax.intuit.com/tax-tools/calculators/taxcaster