addition, we experienced a decrease of $287,221 in operating, maintenance and management expenses at the multifamily properties held throughout both periods primarily due to the decrease in reimbursements to affiliates as a result of the Internalization Transaction.
Real estate taxes and insurance
Real estate taxes and insurance expenses were $47,892,607 for the year ended December 31, 2020, compared to $25,152,761 for the year ended December 31, 2019. The increase of $22,739,846 was primarily due to the increase in the number of properties in our portfolio subsequent to December 31, 2019. In addition, we experienced an increase of $739,347 in real estate taxes and insurance expenses at the multifamily properties held throughout both periods.
Fees to affiliates
Fees to affiliates were $30,776,594 for the year ended December 31, 2020, compared to $25,861,578 for the year ended December 31, 2019. The increase of $4,915,016 was primarily due to an increase in investment management fees, property management fees, loan coordination fees and the reimbursement of onsite personnel during the year ended December 31, 2020, primarily as a result of the increase in the number of properties in our portfolio subsequent to December 31, 2019. We expect these amounts to decrease in future periods as a result of costs savings in connection with the Internalization Transaction.
Depreciation and amortization
Depreciation and amortization expenses were $162,978,734 for the year ended December 31, 2020, compared to $73,781,883 for the year ended December 31, 2019. The increase of $89,196,851 was primarily due to the net increase in depreciable assets of $1,493,091,796, including the increase in tenant origination and absorption costs of $1,752,793 subsequent to December 31, 2019, as a result of the increase in the number of properties in our portfolio subsequent to December 31, 2019. In addition, we experienced an increase of $1,209,997 in depreciation expenses at the properties held throughout both periods. We expect these amounts to increase slightly in future periods as a result of anticipated future enhancements to our real estate portfolio.
Interest expense
Interest expense for the year ended December 31, 2020, was $75,171,052 compared to $49,273,750 for the year ended December 31, 2019. The increase of $25,897,302 was primarily due to the increase in the notes payable, net, of $1,020,686,626 since December 31, 2019. The increase in notes payable, net consists of the following: (1) $791,020,471 that relates to the assumption of notes payable pursuant to the Mergers, (2) $81,315,122 that relates to the debt assumed on the acquisitions of two multifamily properties subsequent to December 31, 2019, (3) $198,808,000 that relates to the increase in borrowings pursuant to the MCFA and PNC MCFA subsequent to December 31, 2019, (4) $6,264,549 that relates to proceeds from the issuance of mortgage notes payable during the year ended December 31, 2020, and (5) $3,809,734 that relates to debt premiums, net of accumulated amortization and debt discounts, net of accretion, offset by a decrease in notes payable, net consisting of the following: (1) $4,485,637 that relates to the payment of principal on existing debt since December 31, 2019, (2) $51,260,000 that relates to the payoff of principal debt in connection with the sale of real estate assets during the year ended December 31, 2020, and (3) $4,785,613 that relates to deferred financing costs, net of accumulated amortization subsequent to December 31, 2019.
Included in interest expense is the amortization of deferred financing costs of $1,948,437, net, unrealized loss on derivative instruments of $65,391, amortization of net debt premiums of $(1,393,673), interest on capital leases of $175, closing costs associated with the refinancing of debt of $42,881, credit facility commitment fees of $65,953, net of capitalized interest of $807,345, for the year ended December 31, 2020. The capitalized interest is included in real estate held for development on the consolidated balance sheets. Our interest expense in
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