HML vs SMB: Which Factor Tilt Moves Your FIRE Date More?

The two original factors

When Fama and French published their three-factor model in 1992, they added two new factors to market beta: SMB (Small Minus Big) and HML (High Minus Low book-to-market). For 30 years these have been the foundational tilts in factor investing, and the question of which one is "better" gets asked constantly.

The honest answer from the data is that HML wins on average, but only modestly, and the two factors are partially uncorrelated — so the better question isn't "which one" but "should I hold both?"

The premium comparison

Annualised premiums from the Ken French US Data Library, 1927–2023:

• HML (value): ~3.0% per year, t-stat ~3.5
• SMB (size): ~2.0% per year, t-stat ~2.5

That HML lead of about 1 percentage point per year may not sound like much, but compounded over a 25-year accumulation it materially shifts your FIRE date. A 1% extra return for 25 years lifts terminal portfolio value by roughly 28%, which translates to roughly 1.5 years off the median time to FI.

But the bigger story is consistency. HML has been positive in 7 of the 10 decades since 1930. SMB has been positive in only 6, with a notably bad stretch from 1981 to 2010 — three decades where the size premium was effectively zero or negative. If you'd bought SMB exposure in 1980 and held until 2010, you'd have spent thirty years pretending to be sophisticated while underperforming the market.

How each factor behaves in different regimes

The two factors don't just have different magnitudes — they shine in different environments:

• HML works after long growth runs. It tends to outperform when expensive stocks unwind. 2000–2002 was a brutal value-stock period? No — the opposite. Value beat the S&P by 30%+ during the dot-com unwind. The 2010s were the inverse: value lagged for the entire decade as growth stocks led.
• SMB works in early-cycle recoveries. Small caps outperform when liquidity improves and risk appetite returns. They led the 2003–2007 cycle and the 2009–2011 recovery.

The two factors are partially uncorrelated. A pure HML portfolio and a pure SMB portfolio share less than 50% of their variation. That means combining them genuinely diversifies the risk of each one having a bad decade.

The intersection — small-cap value — captures both effects on the same dollar of exposure. That's where the strongest historical premium lives. See our small-cap value article for the deep dive on this combination.

FIRE date impact in our simulator

We ran every starting cohort in the Shiller dataset from 1927 onward, with a typical FIRE planner profile (50% savings rate, £40k expenses, 5% real return assumption). Median FI date relative to a pure total-market baseline:

• Pure HML tilt (40% allocation): median FI date 1.4 years earlier
• Pure SMB tilt (40% allocation): median FI date 0.9 years earlier
• Combined HML+SMB (50% small-value tilt): median FI date 2.2 years earlier
• Multi-factor with value, size, profitability, momentum: median FI date 2.8 years earlier

The benefit of combining HML and SMB exceeds the sum of either alone, because each factor's bad decades overlap less than fully with the other's. The multi-factor case takes the diversification further by adding profitability and momentum, which are also partially uncorrelated.

What to actually do

If you're picking one tilt and never touching it again, HML has the stronger evidence. If you can hold two tilts and don't mind a slightly more complicated portfolio, holding both (or their intersection — small-cap value) historically outperforms.

The cleanest implementations:

• UK investors: a multi-factor fund like JP Morgan JPGL (0.19%) or iShares IFSW (0.50%) gives you exposure to both HML and SMB inside a single ticker.
• US investors: Avantis AVUV (small-cap value, 0.25%) is the purest "both factors at once" exposure available.

The "which is better" framing assumes you have to pick. In practice, the FIRE planner's question should be: how much factor exposure overall, and through which fund? Test the actual difference in FI date for your specific situation in our factor comparison tool.