What Is the Force Index?

Michael Whitman · Trading since 2017, full-time since 2020 · YouTube creator, 137K subscribers · Published 2026-09-14 · Updated 2026-10-19

Covered on this page: TradingView.

The force index combines price movement and volume into one number. The premise is reasonable and the output requires more handling than most indicators before it says anything.

How it works

Take the change in closing price from one period to the next and multiply it by that period’s volume.

The sign follows the price. A rising close gives a positive value; a falling one gives a negative value, and the magnitude scales with both the move and the volume.

A large move on heavy volume produces a large reading. The same move on light volume produces a small one, which is the distinction the indicator exists to draw.

Why smoothing is not optional

The raw series swings wildly. Volume varies enormously between periods and price changes flip sign constantly, so the product jumps around with no usable pattern.

A short average — two periods is conventional — makes it readable for short-term entries while keeping it responsive.

A longer average — thirteen periods is the common choice — shows the trend in participation rather than individual periods, and the two lengths answer different questions.

A worked example

Take a hypothetical stock that closes 0.50 higher than the period before. On 2,000,000 shares the raw force index is 1,000,000; the same move on 200,000 shares reads 100,000.

Multiply by volume and the result has no natural scale. A force index value means nothing in isolation — it depends on the instrument’s price level and its typical volume.

So readings are compared to the indicator’s own history, not to a threshold. There is no overbought level here in the way there is for a bounded oscillator.

Which is the main practical difference from an indicator like RSI. It has no fixed range, so every interpretation is relative to what this instrument has recently produced.

What people actually look for

A cross of zero on the smoothed line. Participation shifting from net selling to net buying, or the reverse, which is the simplest reading.

Divergence. Price making a new high while the force index does not, suggesting the move happened on less participation than the previous one.

And extremes relative to recent history. An unusually large reading marks a period where a great deal of volume moved price, which often coincides with capitulation or a breakout.

None of those is a signal on its own. The indicator is a description of what already happened — participation is observable only after the fact — and the divergences that look compelling in hindsight are frequent and often resolve by the price simply continuing.

The original data

Real closes change direction constantly. The S&P 500 finished up on 53.1% of trading days from 1950 to 2026 and set a fresh record on only about 7% of them, so even a market that rose for decades spent most days reversing or giving ground.

That constrains what any such indicator can do. With daily direction close to a coin toss, a smoothed measure of participation is describing a pattern that rarely persists long enough to act on.

And each act pays the spread and a commission. An indicator generating frequent signals in a market that flips direction this often is paying that cost repeatedly for moves that may not be there.

What volume does and does not tell you

Volume is a count of transactions, not of conviction. Every trade has a buyer and a seller, so high volume means disagreement was resolved at that price rather than that one side was stronger.

Which undercuts the usual language. “Buying pressure” describes a price that rose, and the volume attached tells you how many shares changed hands while it did — not that buyers outnumbered sellers, since by construction they cannot.

The defensible reading is narrower. A large price move on heavy volume means a lot of ownership changed at the new price, which makes that price more established than one reached on almost no trading.

And that is genuinely useful. It is a smaller claim than most volume indicators are described as making, and it is the part that survives examination.

Where it sits among volume indicators

On-balance volume adds or subtracts the whole period’s volume based on the direction of the close, ignoring the size of the move entirely.

Accumulation-distribution weights volume by where the close sits within the period’s range, which responds to the shape of the bar rather than the change between bars.

Money flow index bounds the same idea between zero and a hundred, which makes it readable against fixed levels in a way this indicator is not.

All of them combine the same two inputs differently, and their signals agree far more often than the differences between them would suggest — which is worth knowing before adding several to one chart and mistaking agreement for confirmation.

How this connects

This multiplies a price change by volume, which puts it in the volume analysis family alongside OBV and money flow tools.

The idea is that a move on heavy volume means more than the same move on nothing - a reasonable claim and one the formula asserts rather than tests.

It is unbounded, so the absolute number means little across instruments; only the slope and the zero line carry information.

Smoothing changes what it is. A short average makes it a bar-to-bar reading; a long one makes it a market trend filter, and those are different tools sharing a name.

And volume data quality decides everything - in fragmented markets the figure depends on which venues your feed consolidates.

When it fails

The characteristic failure is reading divergence as a reversal signal. Price makes a new high, the force index makes a lower one, and the interpretation is that the move lacks support and will turn. It frequently does not — a trend can continue for a long time on declining participation, because the people who wanted to sell have already sold and it takes very little buying to keep lifting a thin market. Divergence identifies a condition that is present before some reversals and also present through long stretches of continuation, with nothing in the indicator distinguishing them.

A second failure is comparing readings across instruments, where price levels and volumes differ so the scale is meaningless.

A third is using the raw unsmoothed series, which is noise.

A fourth is treating volume as a measure of intent, when every trade has two sides.

And a fifth is optimizing the smoothing length on past data, which fits the indicator to a period rather than testing it.

Related

Volume analysis covers the wider practice this belongs to. Volume covers what is actually being counted. And market trend covers the direction this indicator is usually read alongside.

This page is educational, not financial advice. Test every idea on your own charts before risking money. Some links on this page earn a commission if you buy through them. It costs you nothing and it does not decide what appears here or in what order — how these pages are made is set out in our methodology.