Momentum Investing (12-1 Month)

What Is the 12-1 Momentum Strategy?

The momentum strategy, in the context of a single asset (like investing in SPY or QQQ), works as follows:

• Each month, calculate the asset's total return over the past 12 months, <strong>excluding the most recent month</strong> (i.e., months T-12 to T-1)
• If the 12-1 month return is positive (the asset is in an uptrend): stay invested / buy
• If the 12-1 month return is negative (the asset is in a downtrend): sell and move to cash
• Rebalance monthly — recalculate and act accordingly each month

The exclusion of the most recent month is critical. Research by Jegadeesh (1990) and others showed that very short-term (1-month) returns actually exhibit reversal rather than continuation — stocks that were up last month tend to be down next month on average. By skipping the most recent month, the strategy avoids this short-term reversal and focuses purely on the intermediate-term momentum signal.

In a cross-sectional context (selecting among multiple assets), the strategy buys the top decile of performers over the past 12-1 months and sells (or shorts) the bottom decile. In our single-asset backtest implementation, it's simplified to a binary invested/cash decision based on whether the asset's own 12-1 month return is positive or negative.

The Academic Foundation: Jegadeesh & Titman (1993)

Narasimhan Jegadeesh and Sheridan Titman published "Returns to Buying Winners and Selling Losers: Implications for Stock Market Efficiency" in the Journal of Finance in 1993. It is one of the most cited papers in financial economics, with over 10,000 academic citations.

Key findings from the original paper:

• US stocks that performed best over the past 3–12 months continued to outperform over the subsequent 3–12 months, generating excess returns of approximately 1% per month
• The effect was strongest for the 6-month and 12-month formation periods
• Winners-minus-losers portfolios (zero-investment strategies) generated 12.01% annual returns in their 1965–1989 sample
• The anomaly was not explained by systematic risk (beta) — it appeared to be a genuine alpha-generating strategy

Subsequent research has confirmed and extended the finding:

• Fama & French (1996) acknowledged momentum as a genuine anomaly not explained by their 3-factor model — it was later incorporated as the 4th factor in the Carhart (1997) model
• Asness, Moskowitz & Pedersen (2013) showed momentum works across 8 different asset classes (stocks, bonds, currencies, commodities) and 40 countries
• AQR Capital Management has commercially exploited momentum since 1998 through long-short equity strategies
• Daniel, Hirshleifer & Subrahmanyam (1998) attributed momentum to investor overconfidence and self-attribution bias — behavioral rather than risk-based

How Monthly Rebalancing Works in Practice

On the first trading day of each month:

• Look up the asset's price 12 months ago and 1 month ago
• Calculate: (Price 1 month ago − Price 12 months ago) / Price 12 months ago
• If this 12-1 month return is positive: hold or buy the asset
• If negative: sell the asset and park in cash (or short-term bonds)
• Repeat next month

A concrete example with SPY:

The strategy automatically exits equities when the asset has been in a sustained 12-month downtrend — which historically corresponds to bear market conditions — and re-enters when the medium-term trend turns positive.

When Momentum Works — and When It Struggles

Pros and Cons

Key Parameters to Tune

Who Should Use the Momentum Strategy?

Momentum is well-suited for:

• Quantitatively inclined investors comfortable with a rules-based approach that may hold cash for extended periods
• Investors who want bear market protection without relying on subjective market analysis
• Long-term investors using tax-advantaged accounts (IRAs, 401ks) where monthly rebalancing doesn't trigger taxable events
• Investors applying the strategy across multiple asset classes (stocks, bonds, commodities, real estate) — the multi-asset version is significantly more powerful

Momentum is less suited for investors in taxable accounts with frequent rebalancing, or for short-term traders who need faster signal responsiveness. The 12-1 momentum factor is specifically a medium-term signal — using it on daily or weekly timeframes destroys its effectiveness.

Real Example: 12-1 Momentum on SPY (2007–2009)

The 2008 financial crisis provides a strong illustration:

• Through 2007: 12-1 momentum signal remains positive → strategy stays invested through the early gains
• January 2008: The 12-month trailing return (Feb 2007–Jan 2008) turns negative as the bear market deepens → strategy exits to cash at ~S&P 1,400
• The S&P 500 continues declining to 676 by March 2009 — avoided by the momentum strategy while in cash
• June 2009: The 12-1 signal turns positive (March 2008–June 2009 return finally positive due to recovery from March 2009 bottom) → strategy re-enters at ~S&P 940
• Net effect: sold at ~1,400, rebought at ~940 — avoided the bulk of the 50%+ crash despite the late re-entry

The 2020 comparison: the March 2020 crash was too fast for the 12-1 signal to catch — the strategy stayed invested through the decline but also captured the full recovery. A different risk/reward profile depending on the nature of the bear market.

Try It Yourself — Strategy Backtester

See how the 12-1 Momentum strategy would have performed on any US stock or ETF over the past 1–20 years. Compare momentum against DCA, RSI, MA Crossover, Value Averaging, and 3 other strategies side by side.