Operating Expenses
Our operating expenses are classified into three categories: research and development, sales and marketing, and general and administrative. For each category, the largest component is personnel costs, which consists of salaries, employee benefits (including commissions and bonuses) and share-based compensation expense. Operating expenses also include allocated overhead costs for facilities as well as depreciation and amortization. Allocated costs for facilities primarily consist of rent and office maintenance and utilities. We expect personnel and all allocated costs to continue to increase in absolute dollars as we hire new employees and add facilities to continue to grow our business.
Research and Development. Research and development expenses increased by $9.8 million, or 23.5%, from $41.8 million in the nine months ended September 30, 2018 to $51.6 million in the nine months ended September 30, 2019. This increase was primarily attributable to a $6.9 million increase in personnel costs and related expenses, as we increased our research and development team headcount to support continued investment in our future product and service offerings. The increase was also attributable to a $0.8 million increase in the use of third party consultants and to a $0.8 million increase in software and related expenses.
Sales and Marketing. Sales and marketing expenses increased by $23.2 million, or 21.5%, from $108.0 million in the nine months ended September 30, 2018 to $131.2 million in the nine months ended September 30, 2019. This increase was primarily attributable to an $18.1 million increase in personnel costs and related expenses due to increased headcount in all regions to expand our sales and marketing organization. The increase was also attributable to a $3.1 million increase in expenses related to our marketing programs.
General and Administrative. General and administrative expenses increased by $6.8 million, or 23.1%, from $29.5 million in the nine months ended September 30, 2018 to $36.3 million in the nine months ended September 30, 2019. This increase was primarily attributable to an increase of $5.7 million in personnel costs and related expenses due to increased headcount coupled with a $0.4 million increase in services fees due to external legal counsels, accounting and insurance costs and a $0.5 million increase in depreciation of fixed assets expenses.
Financial Income, Net. Financial income, net changed by $1.9 million from $3.5 million of income in the nine months ended September 30, 2018 to $5.4 million of income in the nine months ended September 30, 2019. This change resulted primarily from an increase of $3.8 million in interest income from investments in marketable securities and short and long-term bank deposits, offset by a $1.8 million loss from foreign currency exchange differences.
Taxes on Income. Taxes on income increased from $0.4 million in the nine months ended September 30, 2018 to $2.4 million in the nine months ended September 30, 2019. Our effective tax rate was 1.5% in the nine months ended September 30, 2018 and 5.4% in the nine months ended September 30, 2019. The higher effective tax rate in the nine months ended September 30, 2019 in comparison to the nine months ended September 30, 2018 was mainly attributable to excess tax benefit related to share based compensation, which lowered the effective tax rate in the nine months ended September 30, 2018, partially offset by intra-entity intellectual property transfer tax expenses.
Liquidity and Capital Resources
As of September 30, 2019, we had $555.1 million of cash, cash equivalents, short-term bank deposits and marketable securities. This compared with cash, cash equivalents, short-term bank deposits and marketable securities of $451.2 million as of December 31, 2018. We believe that our existing cash, cash equivalents, short-term bank deposits and marketable securities will be sufficient to fund our operations and capital expenditures for at least the next 12 months. Our future capital requirements will depend on many factors, including our rate of revenue growth, the expansion of our sales and marketing activities, the timing and extent of spending to support product development efforts and expansion into new geographic locations, the timing of introductions of new software products and enhancements to existing software products and the continuing market acceptance of our software offerings.