EMA vs SMA

Michael Whitman · Trading since 2017, full-time since 2020 · Published 2026-09-08 · Updated 2026-10-19 · Reviewed 2026-10-04

Two ways of averaging the same closes. The simple one treats every close in its window equally; the exponential one leans on the newest. That difference is exact, it can be written in one line each, and on the S&P 500 it shows up most clearly in the famous 50/200 crosses.

What each one is

The simple moving average (SMA) of length N is the sum of the last N closes divided by N. Each close in the window carries the same weight, 1/N, and the close that leaves the window drops to zero at once. Simple moving average covers it.

The exponential moving average (EMA) of length N gives today’s close a weight of 2/(N+1) and the previous EMA the rest: EMA today = 2/(N+1) × close + (1 − 2/(N+1)) × EMA yesterday. It needs a starting value; the usual one, used by StockCharts and here, is the simple average of the first N closes. Exponential moving average covers that calculation.

So both summarize closes already printed. Neither turns ahead of price; the gap between them is how fast old closes stop counting.

Where they differ

How the weight is spread. For a 50-day line the exponential version gives the newest close 3.92% and the simple one 2.00%. For a 200-day line it is 0.995% against 0.50%. Closes older than N sessions carry none of a simple average and about 13.5% of an exponential one, whatever the length.

How each reacts to a close leaving the window. The simple line can jump on a quiet day when an old, extreme close drops out. The exponential line has no such edge, because nothing drops out at once.

How much they disagree. On the S&P 500 since 1960 the two 50-day lines sat a median 0.49% apart and the two 200-day lines 0.93% apart. The close was above one 50-day line and below the other on 878 sessions (5.23%).

Who watches which. The golden and death crosses are usually quoted on simple 50- and 200-day lines, as the death cross page notes, so those are the levels most readers are looking at.

Which one to use: EMA or SMA?

Use the simple version when the level matters because others quote it, such as the 200-day line.

Use the exponential version when you want a line that responds sooner to a turn upward and you can accept more reversals, as the cross counts below show.

Use the same type throughout a test. Swapping type changes the cross dates by days or weeks, so a rule tested on one and traded on the other is a different rule.

And set the length first. A 50 and a 200 differ far more from each other than a simple 50 differs from an exponential 50.

The 50/200 cross in both versions

The test. Every daily close of the S&P 500 since it took its 500-stock form on 4 March 1957, through 2 October 2026. Crosses are counted from 4 January 1960, once the exponential lines have settled (next section). A cross is a session when the 50-day line ends on the other side of the 200-day line from the session before.

Same number, different dates. Over 66.74 years the simple pair crossed 68 times and the exponential pair 68 times, 34 upward each. Matching each simple cross to the nearest exponential cross in the same direction within 120 sessions paired 54 of them; 14 simple crosses had no exponential partner and 16 exponential crosses had no simple one.

Upward, the exponential cross usually came first. Of 26 matched upward crosses, often called golden crosses, the exponential one came first in 20, a median 11 sessions sooner. Downward, it usually did not. Of 28 matched death crosses, it came first in only 9, and the median was 2 sessions later. Both of the exponential lines move faster, and in a decline the faster 200-day line drops toward the 50-day line too, which can delay their meeting.

The exponential pair reversed itself more. 10 of its crosses were followed by another within 20 sessions, against 4 for the simple pair.

A recent pair of each. In 2025 the simple death cross came on 14 April and the exponential one on 11 April, a session earlier. The simple golden cross came on 1 July and the exponential one on 19 May, 29 sessions earlier.

Why the starting value matters

An exponential average never forgets its seed; the seed’s influence fades. Started on the S&P 500’s first 500-stock close on 4 March 1957, a 200-day exponential line seeded with that single close differed by 2.36% from the standard version seeded with the simple average of the first 200 closes, on 16 December 1957 when the standard one begins.

The gap shrank below 1% after 91 sessions, below 0.1% after 304 and below 0.01% after 522, on 12 January 1960. Two platforms showing a long exponential line on a short history can disagree for months for this reason alone.

The original data

The sample. Yahoo Finance’s ^GSPC daily closing values, price only, over that whole span, with crosses counted from 4 January 1960. The definitions are the ones stated above, as StockCharts gives them.

The file. Every simple and exponential 50/200 cross since 1960, with both lines’ values and each simple cross’s matched exponential date and lead in sessions, is in the S&P 500 crosses file. The seed comparison is recomputed from the raw daily download by the same script.

What it does not show. What the index did after any cross, or any trading result. Sixty-eight crosses in 66 years is a small sample, and the 120-session pairing window is a choice; the moving average page counts how often price crossed single lines of each length.

When it fails

The failure is switching type after a losing run. The simple 50/200 cross came late on the last upturn, so the trader moves to exponential lines. The next signal is a downturn, where the exponential cross arrived no sooner on the S&P 500 and reversed itself more often, so the switch buys a whipsaw rather than speed. Each change is made right after the old setting’s weakness showed, which is when the new one meets the conditions it handles worst.

The second failure is plotting both and treating agreement as a second opinion. It is one calculation weighted two ways.

A third is comparing a long exponential line on a short history with one on a long history.

A fourth is expecting either to lead price. Both average what already happened.

And a fifth is trading a quoted level with a different formula. The quoted one is usually simple.

Related

Exponential moving average covers the weighted version. Simple moving average covers the equal-weighted one. And moving average crossover covers the system built on either of them.

This page is educational, not financial advice. Test every idea on your own charts before risking money.