Price tells you where the market went. Volume tells you how much conviction carried it there. The Force Index, introduced by Dr. Alexander Elder in his 1993 classic Trading for a Living, multiplies the two into a single oscillator that measures the force — the punch — behind every bar. It is one of the simplest volume-based indicators to compute, and one of the most underused.
The formula
For each bar:
Force Index = (Close – Previous Close) × Volume
That raw value is noisy, so Elder smooths it with an EMA. Two settings do different jobs:
The logic of the multiplication is intuitive. A big price advance on big volume produces a strongly positive reading — real buying pressure. The same advance on thin volume produces a modest reading — a move nobody backed. A flat close produces zero force regardless of volume, because nobody won the bar.
How Elder uses it
The classic play combines both versions in the spirit of Elder's triple screen approach:
A useful extra: watch for force spikes. An extreme FI(2) reading — several times its normal range — often marks a climax: panic selling near bottoms, euphoric buying near tops. Rather than chasing the spike, mark it as a likely exhaustion zone.
What to watch out for
Force Index vs OBV and Chaikin Money Flow
All three marry price and volume, but differently. OBV keeps a running cumulative total, making it a long-memory trend tool. Chaikin Money Flow measures where the close sits within the bar's range, weighted by volume, over a window. The Force Index is the most momentum-like of the three: it reacts bar by bar to the product of price change and volume, which makes it the best of the family for timing entries inside a trend rather than diagnosing long accumulation.
Bottom line
The Force Index answers a question price alone cannot: was that move pushed, or did it just drift? Traded with Elder's two-EMA discipline — slow line for direction, fast line for timing, divergences for warnings — it turns raw volume into something actionable without adding a single exotic input. Simple formula, honest signal.
The formula
For each bar:
Force Index = (Close – Previous Close) × Volume
That raw value is noisy, so Elder smooths it with an EMA. Two settings do different jobs:
- FI(2) — a 2-period EMA. A fast, twitchy line used for timing entries within an established trend.
- FI(13) — a 13-period EMA. A slower line used to identify the trend of force: who is actually in control, buyers or sellers.
The logic of the multiplication is intuitive. A big price advance on big volume produces a strongly positive reading — real buying pressure. The same advance on thin volume produces a modest reading — a move nobody backed. A flat close produces zero force regardless of volume, because nobody won the bar.
How Elder uses it
The classic play combines both versions in the spirit of Elder's triple screen approach:
- Step 1 — direction from the slow line. FI(13) above zero and rising: bulls are in control, look for longs only. FI(13) below zero and falling: bears own the tape, look for shorts only.
- Step 2 — timing from the fast line. In an uptrend, wait for FI(2) to dip below zero — a brief flush of selling pressure, i.e. a pullback — and buy when it turns back up. In a downtrend, mirror it: sell when FI(2) spikes above zero and rolls over.
- Step 3 — divergences for exits and reversals. Price makes a new high but FI(13) makes a lower high: the rally is advancing on shrinking force, and the trend is suspect. These divergences are among the strongest signals the indicator produces.
A useful extra: watch for force spikes. An extreme FI(2) reading — several times its normal range — often marks a climax: panic selling near bottoms, euphoric buying near tops. Rather than chasing the spike, mark it as a likely exhaustion zone.
What to watch out for
- Volume quality matters. On futures and stocks, volume is real and the Force Index is at its best. In spot forex, platforms substitute tick volume (number of price changes). It correlates reasonably well with true activity, but treat readings with an extra grain of salt — especially during rollover hours and holiday sessions.
- One giant print can dominate. An earnings bar or a news candle with abnormal volume will distort the EMA for several bars. Recognize the outlier and do not read it as a regime change by itself.
- It is not a standalone system. Force Index tells you about pressure, not about levels. Combine it with structure — support, resistance, trendlines — and let the risk plan decide the position size, not the indicator.
Force Index vs OBV and Chaikin Money Flow
All three marry price and volume, but differently. OBV keeps a running cumulative total, making it a long-memory trend tool. Chaikin Money Flow measures where the close sits within the bar's range, weighted by volume, over a window. The Force Index is the most momentum-like of the three: it reacts bar by bar to the product of price change and volume, which makes it the best of the family for timing entries inside a trend rather than diagnosing long accumulation.
Bottom line
The Force Index answers a question price alone cannot: was that move pushed, or did it just drift? Traded with Elder's two-EMA discipline — slow line for direction, fast line for timing, divergences for warnings — it turns raw volume into something actionable without adding a single exotic input. Simple formula, honest signal.