RSI Calculator - Wilder and SMA

An RSI calculator turns a series of closing prices into a 0 to 100 momentum reading called the relative strength index, so you can quickly see when recent gains have dominated recent losses. Use it to scan a stock or ETF chart for overbought or oversold extremes, confirm a momentum shift, sanity-check a long series, or compare a Wilder reading with a simple moving average reading on the same data.

• • Stock overbought scan: Paste a few weeks of daily closes and check whether the latest RSI sits at or above 70.
• • ETF pullback review: Run a 14-period RSI on a broad-market ETF to flag oversold stretches worth a closer look.
• • Method comparison: Switch between Wilder smoothing and a simple moving average on the same series.
• • Audit and journal: Use the supporting gain, loss, relative strength, and parsed-price count as an audit trail.

RSI is a momentum oscillator, not a buy or sell system. It compares the size of recent upward moves with the size of recent downward moves over a fixed lookback and remaps the result onto a 0 to 100 scale.

Paste closing prices from oldest to newest. The output gives you the latest RSI, a signal label, the supporting average gain and average loss, the relative strength ratio, the most recent parsed price, and the parsed price count.

When a Wilder RSI read suggests a momentum shift, the Moving Average Calculator helps you compare it against a smoothed price average on the same series.

The calculator splits the price series into per-period changes, separates each change into a gain or a loss, smooths the two series with the selected method, and combines the smoothed averages into the 0 to 100 RSI value.

• prices: The pasted closing prices entered from oldest to newest. The calculator derives the per-period changes internally.
• N: The RSI lookback period. Wilder's 1978 indicator uses 14. The calculator accepts any integer from 2 to 100.
• gain: The positive portion of a per-period price change. Down moves contribute 0 to the gain series.
• loss: The positive magnitude of a per-period price decline. Up moves contribute 0 to the loss series.
• Average Gain, Average Loss: Smoothed gain and loss averages. Wilder uses recursive exponential smoothing; SMA uses a flat simple average.
• RS: Relative strength. The smoothed average gain divided by the smoothed average loss. RSI remaps RS onto a 0 to 100 scale.

Wilder smoothing is the default because it is the method J. Welles Wilder Jr. introduced in 1978. The first average is the simple average of the first N gains and losses; each new average is (prior average times N minus 1 plus the current value) divided by N.

The SMA option keeps the same gain and loss split but recomputes a flat simple average over the most recent N changes. SMA is easier to audit by hand when the goal is to summarize just the latest window.

When the smoothed average loss reaches 0, RSI = 100. When both smoothed averages are 0, the calculator returns a neutral 50.

According to Investopedia, the relative strength index compares the magnitude of recent gains to recent losses over a lookback window and uses 70 and 30 as standard overbought and oversold thresholds

An RSI value tells you about momentum, not total performance, so pairing the read with the Average Return Calculator gives you a return baseline for the same window.

These four ideas shape how the RSI reads and how you should react to the result.

The threshold label matters more than the exact number. A drop from 60 to 25 is a much bigger story than a drop from 55 to 50. Use the signal label as a quick filter, then read the supporting gain, loss, and price for context.

Wilder reflects a long memory of prior changes; SMA looks only at the most recent N changes. Switching between them on the same series is a quick way to see how much the read depends on the smoothing rule.

Oversold RSI readings often appear near fibonacci support levels, and the Fibonacci Retracement Calculator helps you map those chart levels onto the same price series.

Start with clean, ordered price data, then choose the period and smoothing method that match the question you are asking.

1. 1 Gather closing prices: Pull daily, hourly, or weekly closes from a reliable source in chronological order.
2. 2 Paste the series: Enter the prices separated by commas, spaces, semicolons, or line breaks.
3. 3 Choose the period: Use 14 for a default Wilder review, a shorter period for fast momentum, or a longer period for slower regime reads.
4. 4 Pick Wilder or SMA: Use Wilder to match most charting platforms. Use SMA to audit the most recent N changes without recursive weighting.
5. 5 Read the result: Look at the latest RSI first, then the Overbought, Oversold, or Neutral label, and finally the supporting gain, loss, and price.
6. 6 Document the read: Save the parsed price count, period, method, and signal label so the same calculation can be reproduced later.

With the Wilder 14 default on a 21-day rising-then-dipping series, the calculator returns an RSI near 62.88 and a Neutral signal. Switching to a 5-period Wilder reading on the same series gives a much more sensitive number, which is a useful way to see how much the period choice matters.

Before reacting to a stretched RSI reading, the Beta Stock Calculator gives you a quick read on how volatile the underlying asset is relative to the broad market.

An RSI calculator is most useful when it improves a specific decision or review process.

• • Faster momentum scan: Read the latest value and signal in a single pass without rebuilding a spreadsheet.
• • Method discipline: Use the same period and smoothing rule across assets so you compare like with like.
• • Auditable numbers: Show the average gain, average loss, relative strength, and parsed price count so other people can verify the RSI by hand.
• • Cross-tool pairing: Combine an RSI read with a moving average or fibonacci retracement read to reduce the risk of reacting to one indicator in isolation.
• • Plain-language readout: Pair the numeric RSI with an Overbought, Oversold, or Neutral label so non-technical readers can follow the result.

The benefit is not that an RSI reading tells you what to do. The benefit is that it sorts a noisy price series into a small set of named states that you can reason about and document.

Switching between Wilder and SMA on the same data is also useful. If the two readings disagree by more than a few points, the series is probably in a transitional zone where one or two extra gains or losses can flip the signal.

Pairing an RSI overbought read with the CAPM Calculator helps you separate a momentum stretch from a fundamental expected-return view on the same asset.

The same RSI formula can produce very different readings when the inputs, period, and market context change.

• • RSI is a momentum oscillator, not a forecast. It can stay at the 70 or 30 boundary for weeks during a strong trend.
• • Wilder uses the standard 1978 smoothing rule and SMA uses a flat simple average. Other platforms may use different conventions, so cross-check before quoting the number.
• • The calculator does not adjust for dividends, splits, trading costs, taxes, liquidity, or benchmark selection. Treat the read as one signal among many.

Use the result as one input in a broader review. A Neutral RSI on a stock that just broke out of a long basing pattern is not a contradiction. RSI measures momentum, not structure.

For longer reviews, document the period, smoothing method, data source, and parsed price count so the same calculation can be replayed later.

According to Charles Schwab, the relative strength index is a momentum oscillator bounded between 0 and 100, with 14 periods as the most common setting and 70 and 30 as the conventional overbought and oversold reference levels

According to Fidelity Investments, Wilder's smoothing for the relative strength index updates each new average as (previous average times N minus 1 plus current value) divided by N

An oversold RSI label can hide the size of the actual drawdown, so the Maximum Drawdown Calculator gives useful risk context before treating the signal as a turning point.