NOTE 10. RENTAL INCOME

During the year ended December 31, 2019, approximately 94% 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 6% was related to commercial properties, which have minimum future annual rental income on non‑cancellable operating leases at December 31, 2019 as follows:


	Commercial
	Property Leases
2020	$	2,826,000
2021		2,291,000
2022		1,871,000
2023		1,117,000
2024		459,000
Thereafter		680,000
	$	9,244,000

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 $629,000, $784,000 and $642,000 for the years ended December 31, 2019, 2018 and 2017 respectively. Staples and Trader Joes, tenants at Staples Plaza are approximately 29% 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 December 31,	expiring leases		for expiring leases	leases expiring	expiring leases
2020	$	232,238	12,982	14	8	%
2021		835,995	40,586	7	29	%
2022		580,954	15,330	9	20	%
2023		444,280	13,591	6	15	%
2024		623,739	20,709	11	21	%
2025		64,657	1,106	1	2	%
2026		—	—	—	—	%
2027		—	—	—	—	%
2028		—	—	—	—	%
2029		142,450	3,850	1	5	%
2030		—	—	—	—	%
2031		—	—	—	—	%
Totals	$	2,924,313	108,154	49	100	%

Rents receivable are net of an allowance for doubtful accounts of approximately $240,000 and $532,000 at December 31, 2019 and 2018. Included in rents receivable at December 31, 2019 is approximately $106,000 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 December 31, 2019 also includes approximately $112,000 representing the deferral of rental concession primarily related to the residential properties.