Mercer Advisors buys Fifteenth to bring AI into complex tax work

Mercer Advisors is adding AI software and specialized tax professionals to help its teams serve more clients with complicated finances. The wealth manager announced on November 5, 2026, that it had acquired Fifteenth, a tax and accounting firm whose proprietary platform focuses on equity compensation and other complex tax situations.

The transaction brings Fifteenth’s technology builders and tax team into a national business reporting $114 billion in client assets as of September 30. That figure includes assets under management, assets under advisement and certain recently acquired assets. Mercer plans to integrate Fifteenth’s tools alongside its existing tax infrastructure.

Built around stock-based wealth

Fifteenth pairs annual tax preparation with year-round planning, rather than limiting its service to filing season. Its team brings experience from Big Four accounting firms and other leading practices. The company has built a following among employees of Silicon Valley technology businesses, with tools designed for several specific situations:

• Exercising stock options and planning around the resulting tax situation.
• Tender offers and other events that allow clients to turn holdings into cash.
• Tax filings involving multiple entities, alongside ongoing planning for complex financial circumstances.

Fifteenth CEO and co-founder Ankur Dahiya said its specialized tools already serve more than 1,000 professionals. Mercer’s chief platform officer, Cynthia Loh, said the technology had been built and refined through supporting thousands of returns. Those are company descriptions of its existing use, not measurements of the benefits Mercer will achieve after integration.

We built Fifteenth around a simple idea: even the most complex tax situations shouldn’t have to feel complex for the client. Technology is a huge part of how we deliver on that promise, but so is the judgment of experienced tax professionals.

Laura Moreno, chief tax officer and co-founder of Fifteenth

More capacity, alongside more tax staff

Mercer’s integration plan centers on increasing the capacity of its tax teams while maintaining personalized service. Loh described the expected gain as meaningful, but the announcement did not quantify a target for faster work or additional clients. The stated model keeps specialized professionals alongside the technology, rather than presenting software as a replacement for their expertise.

Tax professionals already account for roughly one in 10 Mercer employees. The firm expects that share to reach one in eight by the end of 2026. Its announcement pairs that expected staffing shift with the plan to use Fifteenth’s technology to support more clients whose needs require specialized tax work.

A relationship before the sale

Mercer says more than half of the ultra-high-net-worth clients joining the firm actively seek tax capabilities within a unified advisory service. It attributes that demand to increasingly complex wealth and a wave of executive equity and liquidity events at fast-growing companies. Fifteenth adds expertise aimed directly at those circumstances.

The acquisition also gives Mercer an opportunity to establish planning relationships before a business sale, initial public offering or another major cash-generating event. Mercer describes that earlier engagement as a benefit of Fifteenth’s equity-compensation focus. It says the incoming team and technology will also deepen support for existing Mercer tax clients facing similar complexity.

For Fifteenth’s existing clients, Moreno framed the deal as a way to connect their tax service with broader wealth management. Mercer’s offering includes investment management, financial planning and estate planning alongside tax work. That connection does not mean every service falls under one agreement: Mercer says tax preparation and filing require a separate agreement defining the services and any additional fees.