TurboTax can handle up to 1,500 transactions per brokerage account in TurboTax Online or 2,000 transactions in TurboTax CD/Download. Beyond that, the alternative available is to print Form 8453, which is like a "cover page" and mail in your details within three days of e-filing.
For more information, see: How many stock transactions can TurboTax Online handle?
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