Force Index Indicator: Weighing Price Moves by the Volume Behind Them

Two stocks can close up by the same amount on the same day and still tell you completely different stories. One rose on a trickle of trades. The other rose while lakhs of shares changed hands. The force index indicator exists to separate those two days. It takes the price change, multiplies it by volume, and hands you a single number that says how much muscle was behind the move.

It is one of the simplest volume oscillators you can put on a chart, and that simplicity is the appeal. There is no typical price, no high-low range, no bounded scale. Just close minus previous close, times volume. In this guide we walk through the formula, a full worked example in rupees, the three ways traders read it, and where it lets you down.

What the Force Index Indicator Measures

The force index was created by Alexander Elder, a psychologist and trader, and published in his 1993 book Trading for a Living, according to Investopedia’s force index explainer. Elder’s idea, as StockCharts ChartSchool describes it, is that every price move has three parts: direction, extent and volume. The indicator folds all three into one line.

• Direction sets the sign. Close above yesterday’s close and the reading is positive. Close below and it turns negative.
• Extent is the size of the price change. A ₹10 move counts for more than a ₹1 move.
• Volume is the multiplier that Elder treated as a measure of commitment. A big move on heavy volume shows buyers or sellers who meant it.

The result is an oscillator that swings above and below zero. Unlike RSI, it has no ceiling or floor. Investopedia calls it unbounded, which means it can rise or fall indefinitely. That one detail shapes how you should read it, and we will come back to it.

The Formula, Step by Step

Both sources give the same two-line calculation:

• Force Index (1) = (today’s close − previous close) × today’s volume
• Force Index (13) = 13-period exponential moving average (EMA) of Force Index (1)

The raw one-period version is jagged. It flips sign almost every other day on a normal stock. StockCharts notes that Elder recommends smoothing it with a 13-period EMA to cut down on those positive-negative flips, and Investopedia says 13 periods is the typical setting, though longer settings such as 100 are also used. More periods give a smoother line, which longer-term traders tend to prefer.

For the EMA itself, Investopedia’s EMA page gives the weight on the latest value as smoothing ÷ (1 + number of days), with 2 as the most common smoothing factor. For a 13-day EMA that works out to 2 ÷ 14, or about 0.143. For a 2-day EMA it is 2 ÷ 3, or about 0.667.

A Worked Example in Rupees

Let’s take a made-up NSE stock, call it Stock A, over six sessions. The prices and volumes below are hypothetical, chosen only to show the arithmetic.

Day 2 is straightforward: the stock gained ₹8 on 3,50,000 shares, so Force Index (1) is 8 × 3,50,000 = 28,00,000. We use that as the starting value of the EMA.

Day 3 is where it gets interesting. The stock slipped ₹3, but only 1,20,000 shares traded. The raw reading is −3,60,000. With a 2-day weight of two-thirds, the EMA becomes (−3,60,000 × 2/3) + (28,00,000 × 1/3) = 6,93,333. It drops sharply but stays positive. A one-day dip on thin volume doesn’t erase a strong up day on heavy volume.

Day 4 is the big one. A ₹10 jump on 4,00,000 shares gives +40,00,000, and the EMA climbs back to 28,97,778. Days 5 and 6 repeat the pattern: a small, quiet pullback, then another up day on decent volume. Every down day in this sequence came on light volume, and every up day came on heavier volume. The smoothed line never went negative. That is exactly the picture of buyers in control that the indicator is built to show.

A pullback on thin volume barely dents the force index. A pullback on heavy volume is the one that should make you sit up.

Same move, different force

Now compare two more hypothetical stocks on a single day. Stock B rises ₹20 on 50,000 shares. Stock C rises just ₹4 on 6,00,000 shares.

• Stock B: 20 × 50,000 = 10,00,000
• Stock C: 4 × 6,00,000 = 24,00,000

Stock C’s modest move carries more than twice the force of Stock B’s eye-catching jump. That’s the whole point. Investopedia makes the same observation in plain terms: large price moves that lack volume produce readings that are not as extreme as they would be with heavy volume behind them.

One caution from this example. Because the indicator multiplies by share count, a stock that trades crores of shares a day will throw up far bigger numbers than a thinly traded small-cap. Comparing force index values across two different stocks tells you very little. Compare a stock with its own history instead.

Three Ways Traders Read It

1. Trend confirmation with the zero line

Investopedia’s summary is simple: a rising force index above zero helps confirm rising prices, and a falling one below zero helps confirm falling prices. StockCharts adds that the setting decides which trend you’re looking at. It shows a 13-day force index that is jagged and crosses zero often next to a 100-day version that is smoother and crosses far less, and suggests the 100-day line for the medium- or long-term trend. In its summary, the bulls have the edge when the 100-day force index is positive and the bears have the edge when it’s negative.

On a Nifty 50 stock in a steady uptrend, you’d expect the long-period line to sit above zero for weeks at a time, dipping toward zero during consolidations. Investopedia notes this too: during pullbacks and sideways phases the index tends to drift back toward zero, because both volume and the size of price moves shrink.

2. Breakout confirmation

Breakouts from chart patterns are usually confirmed by rising volume, and since the force index already includes volume, Investopedia says a spike in the direction of the breakout can help confirm it. The flip side matters more. If price pokes above resistance and the force index barely twitches, the move lacks conviction, and Investopedia says that kind of non-confirmation could mean the breakout is more likely to fail. If you trade breakouts on NSE stocks, this is a cheap second opinion. Our guide to technical analysis for Indian stocks covers how resistance levels are drawn in the first place.

3. Divergences

This is the classic oscillator signal. If price makes a higher high but the force index makes a lower high, that’s a bearish divergence, and Investopedia says it warns the price may soon decline. If price makes a lower low while the force index makes a higher low, that’s a bullish divergence.

StockCharts insists on confirmation. A bullish divergence is confirmed when the force index moves into positive territory or price breaks resistance. A bearish one is confirmed when the indicator moves into negative territory or price breaks support. It also points out that a 39-period setting produces fewer, longer-lasting zero-line crosses than the 13-period one, which some traders prefer for divergence work.

Divergences take patience. A stock can make two or three higher highs on fading force before it actually turns. Treat the divergence as a warning light, not a sell order.

Elder’s Pullback Setup: 22-Day EMA Plus 2-Day Force Index

The most practical use of the indicator comes from Elder himself. StockCharts describes his approach: use a 22-day EMA of price to identify the trend, and a 2-day force index to spot short corrections inside it.

• When the 22-day EMA is rising, the trend is up. A 2-day force index dipping below zero marks a short-term pullback, which is a potential buying area.
• When the 22-day EMA is falling, the trend is down. A 2-day force index popping above zero marks a short bounce, which is a potential selling area.

StockCharts calls this an aggressive strategy suited to active traders, and mentions that medium-term traders might experiment with a 100-day EMA and a 10-day force index instead.

There are two ways to time the entry, per the same source. You can act as soon as the 2-day force index turns negative, which may give a better reward-to-risk ratio but leaves you exposed if the correction runs a few more days. Or you wait for the force index to turn positive again, which shows the correction may have ended but costs you a slightly worse price.

Here’s how that might play out on a hypothetical large-cap. The 22-day EMA has been sloping up for a month. The stock then has two red sessions on lighter volume, and the 2-day force index slips below zero. An aggressive trader buys at that point with a stop below the recent swing low. A more cautious one waits a session or two for the 2-day reading to turn positive. Either way, the decision only makes sense because the bigger trend was already up. Without that filter, the same dip could just be the start of a breakdown.

The 2-day force index finds the dip. The 22-day EMA tells you whether the dip is worth buying at all.

Elder also built the Elder-Ray index, which measures bull and bear power against an EMA. Many traders run the two together, since they come from the same way of thinking about trends and pullbacks.

Force Index vs Other Volume Indicators

Investopedia compares it with the money flow index (MFI). Both use price and volume to judge trend strength and spot reversals, but MFI uses the typical price (high + low + close ÷ 3) and is bound between 0 and 100, so it gives different information. The force index uses only closing prices and has no fixed range.

The other obvious comparison is on-balance volume. OBV adds or subtracts a day’s full volume depending only on whether the close was up or down. The force index goes a step further and scales that volume by the size of the price change, so a ₹1 gain and a ₹15 gain no longer count the same.

Where the Force Index Falls Short

• It lags. Investopedia points out that it is built from past data and then averaged, so signals can arrive late. After an upside breakout, the index may take a couple of periods to rally, by which point price may have run well past a sensible entry.
• Short settings whipsaw. Investopedia says shorter settings such as 10, 13 and 20 produce a lot of whipsaws, as moderate price or volume jumps cause big swings in the line.
• Long settings are slow. Settings such as 50, 100 or 150 swing less but react later to price changes.
• Volume spikes distort it. In India, block deals, index rebalancing days and F&O expiry sessions can push volume far above normal for reasons that have little to do with conviction. A single such day can dominate a short-period reading. It’s worth checking the cause before reading too much into one outsized bar.
• No fixed overbought or oversold zones. Because the scale is unbounded, you can’t say a reading of +50,00,000 is “high” without comparing it with the same stock’s past readings.

StockCharts’ advice is the sensible one: use the force index alongside other indicators and analysis, not on its own.

A Practical Checklist Before You Act on It

1. Decide your timeframe first. Use a long setting such as 100 for the bigger trend and a short one such as 2 or 13 for entries.
2. Check that the trend filter agrees, whether that’s a rising 22-day EMA, a positive 100-day force index, or both.
3. On a breakout, look for a force index spike in the same direction. No spike, smaller position or no trade.
4. On a divergence, wait for the confirming zero-line cross or a price break.
5. Scan the volume bars for one-off events such as block deals or expiry days that might be inflating the reading.
6. Set your stop before you enter. The indicator tells you about pressure, not about where you’re wrong.

The force index won’t predict anything on its own. What it does well is answer one honest question about any move on your chart: was there real money behind it? Most of the time, that’s the question worth asking before you put your own money in.

Disclaimer: This article is for educational purposes only and is not investment advice. All stocks, prices and volumes in the examples are hypothetical and used only to explain the calculation. Technical indicators can give false signals. Consult a SEBI-registered investment adviser before making investment decisions.