NOTE 10. RENTAL INCOME

During the three months ended March 31, 2018, approximately 93% of rental income was related to residential apartments and condominium units with leases of one year or less. The majority of these leases expire in June, July and August. Approximately 7% was related to commercial properties, which have minimum future annual rental income on non-cancellable operating leases at March 31, 2018 as follows:


	Commercial
	Property Leases
2019	$	2,662,000
2020		2,213,000
2021		1,943,000
2022		1,290,000
2023		646,000
Thereafter		1,105,000
	$	9,859,000

The aggregate minimum future rental income does not include contingent rentals that may be received under various leases in connection with common area charges and real estate taxes. Aggregate contingent rentals from continuing operations were approximately $223,000 and $166,000 for the three months ended March 31, 2018 and 2017 respectively. Staples and Trader Joes, tenants at Staples Plaza, are approximately 31% of the total commercial rental income.

The following information is provided for commercial leases:


	Annual base				Percentage of
	rent for		Total square feet	Total number of	annual base rent for
Through March 31,	expiring leases		for expiring leases	leases expiring	expiring leases
2019	$	431,751	16,542	12	14	%
2020		458,122	17,135	10	15	%
2021		193,519	4,170	6	6	%
2022		1,137,030	47,591	9	39	%
2023		246,341	7,087	4	8	%
2024		379,670	11,668	4	13	%
2025		—	—	—	—	%
2026		—	—	—	—	%
2027		—	—	—	—	%
2028		—	—	—	—	%
2029		142,450	3,850	1	5	%
Totals	$	2,988,883	108,043	46	100	%

Rents receivable are net of an allowance for doubtful accounts of approximately $605,000 and $644,000 at March 31, 2018 and December 31, 2017. Included in rents receivable at March 31, 2018 is approximately $114,000 resulting from recognizing rental income from non-cancelable commercial leases with future rental increases on a straight-line basis. The majority of this amount is for long-term leases at 62 Boylston Street in Boston, Massachusetts.

Rents receivable at March 31, 2018 also includes approximately $120,000 representing the deferral of rental concession primarily related to the residential properties.