NOI for our Same-Store Community properties decreased 10.4%, or $21.9 million, for the three months ended March 31, 2021 compared to the same period in 2020. The decrease in property NOI was attributable to a 6.4%, or $19.1 million, decrease in property rental income and a 3.3%, or $2.8 million, increase in operating expenses. The decrease in property rental income was primarily driven by a 2.8%, or $7.7 million, decrease in rental rates, a $4.5 million increase in our reserve on multifamily tenant lease receivables, an increase of $3.7 million in rent concessions, an increase of $2.0 million in occupancy loss and 0.9%, or $0.3 million, decrease in reimbursement and ancillary and fee income. Physical occupancy decreased by 0.4% to 96.4% and total monthly income per occupied home decreased 6.0% to $2,116.
The increase in operating expenses was primarily driven by a 17.5%, or $2.2 million, increase in repair and maintenance expense due to the increased use of third party vendors, a 2.7%, or $1.0 million, increase in real estate taxes, which was primarily due to higher assessed valuations, and a 28.2%, or $1.0 million, increase in insurance expense due to increased claims, partially offset by a 9.9%, or $1.5 million, decrease in personnel expense as a result of fewer employees.
The operating margin (property net operating income divided by property rental income) was 68.3% and 71.3% for the three months ended March 31, 2021 and 2020, respectively.
Non-Mature Communities/Other
UDR’s Non-Mature Communities/Other represent those communities that do not meet the criteria to be included in Same-Store Communities, which include communities recently developed or acquired, redevelopment properties, sold or held for disposition properties, and non-apartment components of mixed use properties.
The remaining 5.6%, or $11.3 million, of our total NOI during the three months ended March 31, 2021 was generated from our Non-Mature Communities/Other. NOI from Non-Mature Communities/Other decreased by 18.1%, or $2.5 million, for the three months ended March 31, 2021 as compared to the same period in 2020. The decrease was primarily attributable to a $4.2 million decrease in sold and held for disposition communities, partially offset by an $1.2 million increase in stabilized, non-mature communities NOI due to operating communities acquired in 2021 and 2020, and a $0.7 million increase in acquired communities.
Real estate depreciation and amortization
For the three months ended March 31, 2021 and 2020, the Company recognized real estate depreciation and amortization of $144.1 million and $155.5 million, respectively. The decrease in 2021 as compared to 2020 was primarily attributable to fully depreciated assets in 2021 and 2020.
Gain/(Loss) on sale of real estate owned
During the three months ended March 31, 2021, the Company recognized a gain of $50.8 million from the sale of an operating community located in Anaheim, California. During the three months ended March 31, 2020, the Company did not recognize any gains on the sale of real estate.
Interest expense
For the three months ended March 31, 2021 and 2020, the Company recognized interest expense of $78.2 million and $39.3 million, respectively. The increase in 2021 as compared to 2020 was primarily due to $42.0 million from extinguishment cost from the prepayment of debt during the three months ended March 31, 2021 as compared to zero for the three months ended March 31, 2020.
Inflation
We believe that the direct effects of inflation on our operations have been immaterial. While the impact of inflation primarily impacts our results of operations as a result of wage pressures and increases in utilities and material costs, the majority of our apartment leases have initial terms of 12 months or less, which generally enables us to compensate for any inflationary effects by increasing rental rates on our apartment homes. Although an extreme escalation in costs could have a negative impact on our residents and their ability to absorb rent increases, we do not believe this has had a material impact on our results for the three months ended March 31, 2021.