"This past year has been filled with both achievements to be proud of and challenges to overcome and learn from," said Ralph Hamers, CEO of ING Group. "Following the settlement we reached with Dutch authorities in September 2018, we are continuing our know your customer (KYC) enhancement programme, emphasising regulatory compliance as the key priority. The organisation continues to work hard on enhancing our customer due diligence files and on a number of structural solutions to bring our anti-money laundering activities to a sustainably better level. We're committed to conducting our business with integrity, and regulatory compliance remains the priority for 2019 and beyond.
At the same time, we've maintained the focus on our customers by continuing to create innovative products and services while transforming internally so we can provide customers with a differentiating and efficient banking experience. As we work to accelerate the pace of innovation, fintech fund ING Ventures made several investments. We invested in multibank platform Cobase, for example, which makes it easier and more efficient for international corporate clients to work with multiple banks. We also invested, together with UniCredit, in Axyon AI, an Italian company that helps banks offer better and faster advice to their clients by using artificial intelligence to identify investors most likely to participate in a syndicated loan, for example.
We continued to attract new customers. Our global customer base grew by one million customers over the year to reach 38.4 million, and the number of primary customers increased 9.9% to 12.5 million. Our most recent net promoter scores among customers rank us first in six of our 13 retail markets. Our customer focus is also reflected in our strong commercial results in 2018. Net growth in core lending amounted to €36.6 billion, while net growth in customer deposits was €19.3 billion. ING's full-year underlying pre-tax result rose 4.5% to €7,524 million, reflecting continued business growth at resilient interest margins, despite heightened competition in some of our markets; higher net commission and fee income; and somewhat lower risk costs. ING's full-year underlying return on equity increased from 2017 to 11.2% and the fully loaded CET1 ratio came in strong at 14.5%. We propose a full-year 2018 cash dividend of €0.68 per share, comprising the interim dividend of €0.24 paid in August 2018 and a final dividend of €0.44 per share.
Fourth-quarter underlying operating expenses fell 1.9% year-on-year, but they rose 11.3% from the third quarter, mainly due to higher regulatory costs related to the Dutch banking tax. We stepped up our cost-saving measures, resulting in a four-quarter rolling average cost-to-income ratio of 54.8%. We see a need for further cost discipline as we expect lower lending growth in Wholesale Banking, possible increases in regulatory expenses as well as due to the fact that Financial Markets profitability continues to be challenging.
As we take steps to build a sustainable future for our company and our customers, we've achieved a milestone in our ambition to steer our €600 billion loan book towards the well-below two-degree goal of the Paris Agreement. I'm proud that four major global banks have already joined us in our pledge - together, we have a combined loan book of €2.4 trillion. We believe that banks have a vital role to play in scaling, accelerating and financing the transition towards a low-carbon economy. Together, we are stronger. Supporting this transition, ING successfully issued the largest ever green bond transaction certified under the Climate Bonds Standard, and the largest ever from a European bank. The bonds will fund a green loan portfolio of new and existing loans in renewable energy and green buildings.
We've started 2019 with total dedication to our regulatory and compliance commitments, while always remembering who we're here for - our customers. Empowering them to stay a step ahead in life and in business remains our guiding purpose."