Accounts Receivable - Net

Net accounts receivable consisted of the following:



	December 30, 2018			September 30, 2018
	(in thousands)
Billed	$	463,159		$	464,062
Unbilled	265,974			267,739
Total accounts receivable – gross	729,133			731,801
Allowance for doubtful accounts	(43,464		)	(37,580		)
Total accounts receivable – net	$	685,669		$	694,221

Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable, which represent an unconditional right to payment subject only to the passage of time, include unbilled amounts typically resulting from revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Most of our unbilled receivables at December 30, 2018 are expected to be billed and collected within 12 months. The allowance for doubtful accounts represents amounts that are expected to become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and particular industry conditions that may affect a client's ability to pay.

Once contract performance is underway, we may experience changes in conditions, client requirements, specifications, designs, materials and expectations regarding the period of performance. Such changes result in change orders and may be initiated by us or by our clients. In many cases, agreement with the client as to the terms of change orders is reached prior to work commencing; however, sometimes circumstances require that work progress without a definitive client agreement. Revenue and any corresponding receivable in these cases is recognized based on the policy described in Note 3, "Revenue Recognition" above.

The total accounts receivable at both December 30, 2018 and September 30, 2018 included approximately $74 million related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination. We regularly evaluate all unsettled claim amounts and record appropriate adjustments to operating earnings when it is probable that the claim will result in a different contract value than the amount previously estimated. We recorded no material gains or losses related to claims during the first quarters of fiscal 2019 and 2018.

Billed accounts receivable related to U.S. federal government contracts were $80.3 million and $81.5 million at December 30, 2018 and September 30, 2018, respectively. U.S. federal government contracts unbilled receivables were $99.6 million and $102.7 million at December 30, 2018 and September 30, 2018, respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at December 30, 2018 and September 30, 2018.