5. PATENT COSTS

We amortize intangible assets with definite lives on a straight-line basis over their estimated useful lives, ranging from two to ten years, and review for impairment on a quarterly basis and when events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. We analyze our intangible assets, specifically, capitalized patent costs, on an annual basis for any indicator that an impairment exists. As of September 30, 2019 and December 31, 2018, no impairment existed and no adjustments were warranted.

We capitalized approximately $97,000 and $190,000 of patent costs for the three and nine months ended September 30, 2019 as compared to approximately $16,000 and $95,000 for three and nine months ended September 30, 2018, respectively. Patent costs may be creditable against future royalty revenues. For each period presented below, net patent costs consisted of:

	September 30, 2019			December 31, 2018
Patents	$	1,235,919		$	1,046,216
Accumulated amortization		(673,416	)		(601,738	)
Total	$	562,503		$	444,478

The amortization expense for patents for the three and nine months ended September 30, 2019 was approximately $29,000 and $72,000, respectively, and for the three and nine months ended September 30, 2018 was approximately $19,000 and $54,000, respectively. The estimated aggregate amortization expense for the remaining three months of 2019 and each of the years below is approximately as follows:

October 1, 2019 – December 31, 2019	$	24,000
2020		78,000
2021		61,000
2022		61,000
2023		61,000
Thereafter		278,000
Total	$	563,000