The US Census Bureau  clarifies the difference between new home sales and existing home sales. “New home sales and existing home sales are released each month at about the same time. Many comparisons are made between the two series, but before doing any comparisons, one must be aware of some definition differences that affect the timing of the statistics. “
New Home Sales
“The Census Bureau collects new home sales based upon the following definition: “A sale of the new house occurs with the signing of a sales contract or the acceptance of a deposit.” The house can be in any stage of construction: not yet started, under construction, or already completed. Typically about 25% of the houses are sold at the time of completion. The remaining 75% are evenly split between those not yet started and those under construction. “
Existing Home Sales
“Existing home sales data are provided by the National Association of RealtorsÂ®. According to them, “the majority of transactions are reported when the sales contract is closed.” Most transactions usually involve a mortgage which takes 30-60 days to close. Therefore an existing home sale (closing) most likely involves a sales contract that was signed a month or two prior. “
Given the difference, the indicated trends in New Home Sales would probably lead Existing Home Sales by 30 to 60 days, the length of time it takes for an existing home sale to close from point of contract.
However, New Home Sales are more volatile from the standpoint that it is a much smaller data set as they represent something like 10% the number of Existing Home Sales.