HR BLK tax est showed to if HOH w/2 dep refund $6629, she earned approx. 18000 w/SSA 2 dep $2400, is right?

Used the HR BLOCK tax estimator, for head of household with 2 dependents, with income of 18000, would get a refund of approximately $6629??? Yet only had additional income of $2400 from SSA dependency allotments. Does that refund sound right? Is it possible to receive MORE than ONE PAYS IN???