Can I claim someone as a dependent 1/2 the year if I support them

[Hal_Al]

No. There is no partial year dependent claim allowed. it's all (the whole year) or nothing. if the support you provided for half the year amounts to more than half the person's total support for the whole year, you have met the support test. There are other tests that must also be met. See  https://turbotax.intuit.com/tax-tools/tax-tips/Family/Rules-for-Claiming-a-Dependent-on-Your-Tax-Ret...