LONDON — European banks have been busy.

Financial institutions on the Continent have raised at least 40.7 billion euros, or $52.8 billion, in new capital as of the fourth quarter of last year, according to estimates by Citigroup.

The effort is part of policymakers’ push to increase banks’ core Tier 1 ratios, a measure of a firm’s ability to weather financial shocks, to 9 percent by June. Banks must raise a combined 115 billion euros by the summer to meet that target.

Activity over the next few weeks will add to the tally. Europe’s major banks report earnings in February, and Citigroup said it expected institutions to raise a further 24.6 billion euros through June 2012 through so-called retained earnings, a category that includes reductions in employee bonuses and cuts to overall bank lending.

Deutsche Bank of Germany, for example, could pocket up to 3.6 billion euros in retained earnings over that period, based on Citigroup estimates. The figure would be more than enough to cover the 3.2 billion euro shortfall the European Banking Authority wants the bank to fill by this summer. Similarly, the Citigroup research shows BNP Paribas of France may add 4.1 billion euros through this method from October 2011 to June 2012 — well ahead of its 1.4 billion euro capital-raising target.

“BNP has huge capital needs, but can make the target in one swoop by retaining its shareholder dividend,” said an investment banker at a leading European firm, who spoke on condition on anonymity because he was not authorized to talk publicly.

While some of Europe’s largest financial institutions are likely to fill the capital gap by holding on to their profits, others will have to employ different strategies. So far, the most popular method for raising new money has been through so-called liability management exercises. Citigroup estimated European institutions had raised a combined 16 billion euros through the practice, which involves buying back, or exchanging, hybrid securities — investments that pay dividends like bonds, but can be converted into equity — at a discount from investors.

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