About the RSI Calculator
This RSI calculator computes the Relative Strength Index — J. Welles Wilder’s momentum oscillator — from a list of closing prices. Paste closes from any chart or price export, choose the lookback period (14 is the standard), and it returns the latest RSI, the average gain and average loss behind it, the relative strength ratio, and whether the reading is in overbought or oversold territory. The chart plots the RSI over time with the 70 and 30 reference lines.
Traders use RSI to gauge whether a move is stretched: readings above 70 are traditionally called overbought and below 30 oversold, while the 50 line separates bullish from bearish momentum. It is also handy for checking a platform’s indicator, or for learning exactly how the number is built.
Two averaging methods are offered. Wilder’s original method starts with a simple average of the first n gains and losses and then smooths each new value as (previous × (n − 1) + current) ÷ n; this is what most charting software shows. The simple-average (Cutler) variant uses plain averages of the last n changes. Because Wilder smoothing carries memory of older prices, paste at least two to three times the period for results that match your platform closely.
With the default inputs, the rsi (latest) is 57.92. Change any value above to recalculate instantly.
How to use the rsi calculator
- 1Copy closing prices for the stock, ETF, crypto or index, oldest first.
- 2Paste them into the price box — at least the period plus one.
- 3Keep the period at 14 or change it to suit your timeframe.
- 4Choose Wilder smoothing to match most charting platforms.
- 5Read the latest RSI and signal, and use the chart to spot divergences.
Formula and method
Each period’s change is split into a gain (positive changes, else 0) and a loss (the size of negative changes, else 0). With Wilder smoothing, the first average gain and loss are simple means of the first n changes; every later average is the previous average times (n − 1), plus the current gain or loss, divided by n. RS is the average gain divided by the average loss, and RSI rescales it to a 0–100 range.
The simple-average variant (often called Cutler’s RSI) replaces the smoothing with a plain average of the last n gains and losses, so it does not depend on where the data starts. When the average loss is zero the RSI is 100; when there are no changes at all it is shown as 50.
- n
- Lookback period (14 by default)
- RS
- Relative strength — average gain ÷ average loss
- Avgₜ
- Smoothed average gain or loss at period t
Worked examples
Classic 20-close dataset, 14-period Wilder RSI
The first 14 changes average a gain of 0.2386 and a loss of 0.1000 (RSI 70.46). Five more closes are smoothed in — for example the 0.28 drop on the 16th close becomes (0.1000 × 13 + 0.28) ÷ 14. After the last close the averages are 0.1898 and 0.1379, so RS = 1.376 and RSI = 100 − 100 ÷ 2.376 ≈ 57.92.
Same data with simple averages (Cutler)
Using a plain average of the last 14 changes, the gains total 2.47 and the losses 1.66, so the averages are 0.1764 and 0.1186. RS = 1.488 and RSI ≈ 59.81 — a little higher than Wilder’s value because the older, stronger gains are dropped instead of decayed.
Strong rally, 6-period RSI
Nine changes include only two small down days, so after Wilder smoothing the average gain (1.91) dwarfs the average loss (0.17). RS ≈ 11.39 and the RSI is about 91.9, deep in overbought territory above 70.
Frequently asked questions
What do RSI 70 and RSI 30 mean?+
By Wilder’s convention, an RSI above 70 suggests an asset is overbought after strong gains, and below 30 that it is oversold after heavy losses. In strong trends RSI can stay beyond these levels for a long time, so many traders wait for it to cross back before acting.
Why is the default RSI period 14?+
Wilder used 14 periods in his 1978 book New Concepts in Technical Trading Systems, and it became the standard. Shorter periods such as 7 or 9 make RSI more sensitive and hit extremes more often; longer periods such as 21 or 25 make it smoother.
Why does my RSI not match my broker’s chart?+
Wilder smoothing carries memory of every earlier price, so the value depends on how much history is used. Charting platforms start from far more bars than you might paste here. Paste 100 or more closes and the results will usually match to a decimal place or two.
What is RSI divergence?+
Divergence occurs when price makes a new high but RSI makes a lower high (bearish), or price makes a new low while RSI makes a higher low (bullish). It signals weakening momentum and is often used to anticipate reversals, though it can persist.
Can RSI be used on any timeframe?+
Yes. The formula is the same for 1-minute, daily, weekly or monthly bars — paste closes from the timeframe you trade. Daily 14-period RSI is the most widely watched for stocks, while crypto traders frequently use 4-hour and daily charts.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.