While the mad holiday rush might have you making lists of gifts to buy for your loved ones, another season is fast-approaching: tax-loss selling season.

Tax-loss selling usually takes place near the end of the year when investors hope to write off losses from their stocks to offset paying taxes on income revenue from winning stocks in portfolios.

But if you haven’t already prepared to sell your losing stocks and are waiting to do it in December, you might actually be too late.

According to a new report from CIBC Capital Markets, in the past 30 years tax-loss candidates have grossly underperformed the broader S&P/TSX from mid-November to December 28th, and on average by five per cent. Holding onto your losing stocks longer into December could mean booking bigger losses.

Late December is often the worst time to engage in tax-loss sales, as most firms experience a sudden "mean reversion" when tax-loss selling subsides in January,” says Jeff Evans, executive director of quantitative strategy at CIBC Capital Markets in a note to clients.

He adds that while many tax-loss candidates see a rebound in January, approximately 60 per cent of those firms will likely continue to underperform.

If timing your tax-loss sells seems like a daunting task, Evans points out you can also look at swapping out stocks based on factors or themes.

“A great example of this involves the gold and silver stocks: our quant model suggests swapping Detour Gold, Franco-Nevada and Tahoe (which score poorly in our model) for Barrick, Yamana and Eldorado,” says Evans.