Charles Schwab's total client assets increased $35 billion to $1.68 trillion at the end of April, up 11% from the year-ago quarter and up 2% from March, a reflection of the overall strength of the stock market last month.

But the tax man clipped the firm's net new asset total by $500 million as many new and existing clients had to cut substantial mid-month checks to the IRS. The April decline marks the first monthly decrease since June.

Meanwhile, Schwab's daily average client trades slid 1% from April 2010 to 435,000. The drop-off is even more pronounced considering clients' trading volume increased 16% last month.

Schwab shares trimmed 35 cents, or 2%, to $17.63 in Friday afternoon trading.

In April, Schwab opened more than 83,000 new accounts, down 7% from last year but up 1% sequentially.

Investors cashed out more than $3.3 billion from Schwab money market funds in April and extracted more than $521 million from large-cap mutual funds. However, they injected more than $57 million into small- and mid-cap funds.

Schwab operates more than 300 offices worldwide managing more than 8.1 million client brokerage accounts, 728,000 bank accounts and 1.4 million corporate retirement plan participant accounts.