Operating Expenses
Compensation and related expenses increased $24.8 million, or 12.0%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. The increase related to new partner firms was approximately $3.1 million. Non-cash equity compensation increased $1.2 million primarily associated with incentive unit grants. The balance of the increase of $20.5 million was due primarily to an increase in salaries and related expense, due in part to partner firm-level acquisitions subsequent to the six months ended June 30, 2019 and the result of a full period of expense recognized during the six months ended June 30, 2020 for partner firms acquired during the six months ended June 30, 2019.
Management fees increased $24.4 million, or 17.9%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. The increase related to the new partner firms was approximately $8.8 million. Management fees are variable and a function of earnings during the period. The balance of the increase of $15.6 million was due to the increase in earnings during the six months ended June 30, 2020 compared to the six months ended June 30, 2019, due in part to partner firm-level acquisitions subsequent to the six months ended June 30, 2019 and the result of a full period of earnings recognized during the six months ended June 30, 2020 for partner firms acquired during the six months ended June 30, 2019.
Selling, general and administrative expenses increased $3.4 million, or 3.0%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. New partner firms added approximately $3.4 million.
Management contract buyout of $1.4 million for the six months ended June 30, 2019 related to cash consideration for the buyout of a management agreement of one of our retiring principals whereby the business operations were transitioned to one of our other partner firms.
Intangible amortization increased $11.8 million, or 19.6%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. The increase related to new partner firms was approximately $5.3 million. The balance of the increase of $6.5 million was primarily due to partner firm-level acquisitions.
Non-cash changes in fair value of estimated contingent consideration decreased $26.2 million, or 232.3%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. During the six months ended June 30, 2020, the probability that certain contingent consideration payments would be achieved decreased due to Monte Carlo Simulation changes associated with market conditions and Covid-19, resulting in a decrease in the fair value of the contingent consideration liability.
Depreciation and other amortization expense increased $1.3 million, or 26.9%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. The increase was primarily related to an increase in depreciation and amortization related to fixed assets at our new corporate headquarters.
Other income (expense)
Interest expense decreased $3.6 million, or 13.3%, for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. The decrease was due to lower average interest rates during the six months ended June 30, 2020 as a result of the January 2020 Credit Facility amendment to reduce the interest rate spread on the First Lien Term Loan and lower LIBOR rates.
During the six months ended June 30, 2020, a loss on extinguishment of borrowings of $6.1 million was recognized in connection with the January 2020 Credit Facility amendment.
Income Tax Expense
Income tax expense increased $11.9 million for the six months ended June 30, 2020 compared to the six months ended June 30, 2019. For the six months ended June 30, 2020, we recorded tax expense based on an estimated annual effective tax rate of 24.5%. The estimated annual effective tax rate is primarily related to federal, state and local income taxes imposed on Focus Inc.’s allocable portion of taxable income from Focus LLC.