Economic earnings per share of $4.28 improved 35% year over year and represented the strongest first quarter in our history, primarily driven by EBITDA growth of 23% and ongoing share repurchase activity.
Nearly 20 years ago, we began developing AMG-led distribution resources to complement the existing sales efforts of our affiliates.
We have significantly enhanced our capital position and we repurchased nearly 20% of our shares outstanding.
Adjusted EBITDA of $247 million grew 23% year over year, driven by strong affiliate investment performance and the impact of our growth investments.
Economic earnings per share of $4.28 grew 35% year over year further benefiting from share repurchase activity.
In alternatives, fundraising remains strong at Pantheon, Baring, EIG and Comvest as clients continue to steadily increase private market allocations globally, and we reported net inflows of $2.8 billion in the first quarter.
Overall, our private markets book remains a significant source of earnings growth, accounting for nearly 20% of management fee EBITDA with increasing future carried interest potential.
In U.S. equities, we reported net inflows of $300 million.
In global equities, net outflows of $3.9 billion were driven by redemptions in regionally focused strategies.
These strategies generated $900 million in net client cash flows during the quarter, primarily driven by ongoing demand for muni bond strategy at GW&K and stable growth across our wealth management affiliates.
For the first quarter, adjusted EBITDA of $247 million grew 23% year over year, driven by strong affiliate investment performance.
Adjusted EBITDA included $42 million of performance fees, reflecting outstanding performance in certain liquid alternative strategies.
Economic earnings per share of $4.28 grew by 35% year over year, further benefiting from share repurchase activity.
We expect adjusted EBITDA to be in the range of $210 million to $220 million based on current AUM levels, reflecting our market blend, which was up 3% as of Friday.
Our estimate includes performance fees of up to $10 million and the impact of our newest investments in OCP Asia and Boston Common.
Our share of interest expense was $27 million for the first quarter, and we expect interest expense to remain at a similar level for the second quarter.
Controlling interest depreciation was $2 million in the first quarter, and we expect the second quarter to be at a similar level.
Our share of reported amortization and impairments was $41 million for the first quarter, and we expect it to be $35 million in the second quarter.
Our effective GAAP and cash tax rates were 24% and 20%, respectively, for the first quarter, and we expect similar levels for the second quarter.
Intangible-related deferred taxes were $9 million in the first quarter, and we expect an $11 million level in the second quarter.
Other economic items were negative $15 million and included the mark-to-market impact on GP and seed capital investments.
In the second quarter, for modeling purposes, we expect other economic items, excluding any mark-to-market impact, on GP and seed to be $1 million.
Our adjusted weighted average share count for the first quarter was $43.2 million, and we expect our share count to be approximately $42.4 million for the second quarter.
We expect the business to contribute $0.20 of incremental economic earnings per share in 2021 and $0.33 in 2022, including $16 million of EBITDA in 2022.
In the first quarter, we repurchased $210 million of shares and now have repurchased nearly 20% of our shares outstanding over the past two years.
We are focused on continuing to reduce our share count through repurchases over time, and we remain on track to repurchase $500 million of shares this year.

Summary:
Economic earnings per share of $4.28 improved 35% year over year and represented the strongest first quarter in our history, primarily driven by EBITDA growth of 23% and ongoing share repurchase activity.
Economic earnings per share of $4.28 grew 35% year over year further benefiting from share repurchase activity.
Economic earnings per share of $4.28 grew by 35% year over year, further benefiting from share repurchase activity.