Force Index

Combines price direction, the size of the move, and volume into one line that oscillates around zero.

What it is

The Force Index is a volume-based oscillator developed by Alexander Elder and introduced in his 1993 book Trading for a Living. It tries to capture the "force" behind a price move by combining three things: the direction of the move (up or down), the size of the move, and the volume traded. The result is a single line that swings above and below a zero center line. For the raw, single-bar calculation, a reading above zero means the bar closed higher than the previous close, weighted by that bar's volume, while a reading below zero means it closed lower. The raw calculation is noisy, so most charting platforms apply an exponential moving average to it — a short EMA (often 2) for a fast, sensitive version, and a longer EMA (often 13) for a smoother view; note that once the line is smoothed, its sign reflects recent net force rather than the direction of any single close. It is an educational analysis tool, not a trading signal, and like all indicators it describes past data rather than predicting future prices. Trading carries risk of loss.

How it works

The raw Force Index for a single bar is: (current close − previous close) × volume. When price closes up, the value is positive; when it closes down, the value is negative; a bigger price change or higher volume makes the value larger in magnitude. Because that raw line jumps around a lot, it is almost always smoothed with an exponential moving average. A 13-period EMA of the Force Index is the most commonly cited setting — Elder recommended it — and is used to gauge the longer-term picture, while a 2-period EMA gives a much more responsive line that some traders use to study short-term shifts. The zero line is the natural reference point: it separates net positive force (up closes weighted by volume) from net negative force (down closes weighted by volume).

How traders read it

• Traders often read a value above zero as buying pressure having dominated that period, and a value below zero as selling pressure having dominated — but this describes what already happened, not what comes next.
• Crossings of the zero line are commonly watched as a shift from net positive to net negative force, or vice versa; on a smoothed (e.g. 13-EMA) version these crossings are slower and less frequent than on a 2-EMA version.
• The height or depth of a spike is often interpreted as how much conviction (price move plus volume) was behind a bar — large spikes flag unusually forceful sessions, which traders sometimes treat as worth examining rather than acting on.
• Some traders look for divergence: price making a new high or low while the Force Index does not confirm it, which they read as the move losing volume support. Divergence is an observation, not a prediction.
• The 2-period and 13-period versions are frequently read together — the short one for near-term shifts and the long one for the broader backdrop.

Common settings

A 13-period EMA of the Force Index is the most widely cited setting for the longer-term view (the value Elder recommended), and a 2-period EMA for a fast, sensitive short-term view. The zero line is the standard reference. Many traders display both the 2 and 13 versions together.

Strengths

• Blends price direction, move size, and volume into one figure, so it reflects more than price alone.
• The zero line gives a simple, intuitive reference for net positive versus negative force.
• Flexible: a single EMA-length input shifts it from a fast short-term tool to a smoother trend-context tool.
• Useful for studying divergence between a price move and the volume behind it.

Pitfalls to watch

• It depends entirely on volume data. On instruments without reliable centralized volume — spot forex is the classic example — the indicator reflects only tick volume or broker-specific volume, which can differ across feeds and distort the reading.
• Values are unbounded and not normalized across instruments, so a Force Index of 50,000 on one symbol is not comparable to 50,000 on another, or even on the same symbol across different price or volume regimes.
• The raw (unsmoothed) line is very noisy; reading it without an EMA tends to produce frequent, conflicting zero-line crossings.
• Like all indicators it is lagging and backward-looking — smoothing adds delay, and a zero-line crossing confirms a shift only after it has occurred. Nothing here is predictive, and trading carries risk of loss.
• Large spikes can be driven by single events, gaps, or thin sessions rather than sustained pressure, so a big reading is not automatically meaningful.

Pine v6 example

//@version=6
indicator("Force Index", overlay = false)

length = input.int(13, "EMA Length", minval = 1)

// Raw Force Index: price change weighted by volume
rawFI = (close - close[1]) * volume

// Smoothed with an EMA (educational display only)
fi = ta.ema(rawFI, length)

plot(fi, "Force Index", color = color.blue)
hline(0, "Zero Line", color = color.gray, linestyle = hline.style_dashed)

Pro tip: Because Force Index values are not comparable between instruments or across different volume regimes, traders typically read it relative to its own recent history on the same chart — its swings and zero-line crossings — rather than judging an absolute number as "high" or "low." None of this is advice to act on.

Educational only — not financial advice, not a recommendation to trade. No indicator is predictive; trading involves substantial risk of loss.