The cheapest round trip flights from WAS to PAR for any dates in the next six months were priced from about $540 - $550 and from about $534 - $560 (nonstop). A few lucky people found prices as low as $470.
The best day to depart a roundtrip ticket from Washington D.C. to Paris is Monday, saving $10. The best day to return is Monday, saving up to $10.