The S&P 500 is an index of 500 large US companies. On 16 March 2020, it fell 12.0% in a single day. That was its biggest one-day fall in the ten years to October 2026. It came early in the COVID-19 pandemic.
Most down days look nothing like that. This guide shows how much the index moves on a normal day. It then lists the worst day of each year since 2017 and what happened on it. It ends with a few checks for reading a falling market.
Why is the stock market down today? The stock market falls on news about interest rates, inflation, tariffs (taxes on imports), politics, company results or shocks such as a pandemic. Those were the reasons news outlets gave for the worst day of each year since 2017 on the S&P 500, an index of 500 large US companies.
Most days are small. From October 2016 to October 2026, the S&P 500's median daily move was 0.50%, up or down.
Big falls come in clusters. The index fell 2% or more on 25 days in 2020, but on none in 2017.
Big rises often follow big falls. Eight of the ten biggest one-day rises came within five trading days of one of the ten biggest falls.
What a down day means
A share price is the price of the last trade. It changes when buyers and sellers agree a new one. Our guide to how the stock market works follows an order from an app to the exchange.
In this guide, "the stock market" means the S&P 500. It tracks the value of 500 large US companies, with the biggest counting most. We explain it in What Is the S&P 500? A down day means the index ended trading, at its close, below its close the day before.
A share is a claim on a company's future profits. Its value depends on those profits and on the interest rate used to value them today. Our guide to Discounted Cash Flow shows the sums. So news that changes the outlook for profits or for interest rates can move the whole index in a day.
How much does the S&P 500 move on a normal day?
Source: FRED (SP500); YX Insights
Chart 1 sorts the 2,513 trading days from 4 October 2016 to 2 October 2026 by how far the S&P 500 moved. On 75.8% of days, it moved less than 1% either way. The median move was 0.50%. It rose on 54.7% of days and fell on 45.3%.
Big falls were rare. The index fell 2% or more on 87 days, or 3.5% of all days. It fell 3% or more on 32 days.
Big down days come in clusters
Source: FRED (SP500); YX Insights
Chart 2 counts the days each year when the S&P 500 fell 2% or more. The 2026 bar runs only to 2 October. There were 25 such days in 2020 and 23 in 2022. In 2017 there were none, while 2023 had one.
The 2% falls bunched into a few years. In 2020, the worst day came during the pandemic, according to Axios. In 2022, it came on an inflation report, according to CBS News. That year, the Federal Reserve (Fed), the US central bank, raised its main interest rate. This is the Fed Funds Rate, the rate banks charge each other overnight. The top of its target range went from 0.25% to 4.50%. Consumer Price Index inflation was 8.3% in August.
The S&P 500's worst day in each year since 2017
The table lists the S&P 500's biggest one-day fall in each year from 2017 to 2026, with what news outlets reported on the day.
Date | S&P 500 change | What happened that day | Reported by |
|---|---|---|---|
17 May 2017 | −1.8% | Reports said a memo by James Comey, the former director of the Federal Bureau of Investigation (FBI), suggested President Trump tried to interfere with a federal investigation. | Reuters |
5 Feb 2018 | −4.1% | Signs of higher inflation and interest rates. The jobs report three days earlier showed the fastest wage growth since 2009. | Associated Press; CNN |
5 Aug 2019 | −3.0% | China let its currency fall to its lowest against the dollar in more than a decade. That followed US threats of new tariffs, which are taxes on imports. | Associated Press |
16 Mar 2020 | −12.0% | The COVID-19 pandemic. The day before, the Federal Reserve (Fed), the US central bank, cut its target for its main interest rate to 0% to 0.25%. | Axios; Federal Reserve |
27 Jan 2021 | −2.6% | Large technology companies led the fall as company earnings reports came in. | Associated Press |
13 Sep 2022 | −4.3% | The Consumer Price Index showed inflation of 8.3% for August, above the 8.1% expected. | CBS News |
21 Feb 2023 | −2.0% | The 10-year Treasury yield, the interest rate on a ten-year US government bond, hit a three-month high. Home Depot and Walmart gave weak profit outlooks. | Reuters |
5 Aug 2024 | −3.0% | A weak US jobs report the Friday before. Japan's Nikkei 225 index fell 12.4% after the Bank of Japan raised interest rates. | Associated Press |
4 Apr 2025 | −6.0% | China matched new US tariffs with a 34% tariff on all US imports. | Associated Press |
5 Jun 2026 | −2.6% | A strong jobs report made a Fed rate cut less likely. Chip makers led the fall. | Associated Press |
Source: FRED (SP500); Reuters; Associated Press; CNN; Axios; Federal Reserve; CBS News; YX Insights
The worst of all was 16 March 2020, at 12.0%. Eight of the ten biggest falls in the ten years came between 27 February and 11 June 2020. The other two came on 3 and 4 April 2025.
What moves stocks day to day
The causes in the table fall into four groups:
Data releases. Reports on jobs and inflation come out on set dates. The jobs report in February 2018 showed fast wage growth, according to CNN. The Consumer Price Index (CPI) for August 2022 came in above forecasts, according to CBS News. We explain both in What Is CPI? and What Are Nonfarm Payrolls?
Interest rates and the Fed. Higher expected rates lower today's value of future profits. In June 2026, a strong jobs report made a Fed rate cut less likely, according to the Associated Press. Our guide to what the Fed does covers how it sets rates.
Government policy and politics. Trade disputes over tariffs lay behind the worst days of 2019 and 2025, according to the Associated Press. News about President Trump and a federal investigation lay behind the worst day of 2017, according to Reuters.
Company news and shocks. Large technology companies led the fall in January 2021, as their earnings reports came in, according to the Associated Press. The pandemic lay behind the worst day of 2020.
A big fall, then a big rise: April 2025
Source: FRED (SP500)
Chart 3 shows the S&P 500's daily change from 2 to 11 April 2025. On 2 April, President Trump announced new tariffs. Imports faced a tariff of at least 10%, while some countries faced higher rates. The index fell 4.8% the next day. On 4 April, China replied with a 34% tariff on all US imports. That matched the 34% tariff the US had set on Chinese goods, according to the Associated Press. The index fell 6.0%, its worst day since 2020.
Taken together, the falls from 3 to 8 April left the index 12.1% below its close on 2 April. On 9 April, Trump cut the tariffs on most countries to 10% for 90 days. The index rose 9.5%, its biggest one-day gain since October 2008, according to CBS News. The next day it fell 3.5%, after the White House confirmed a 145% tariff on Chinese imports.
So someone who sold after the falls of 3 and 4 April missed the rise of 9 April. The same pattern shows across the ten years to October 2026. Eight of the ten biggest one-day rises came within five trading days of one of the ten biggest falls.
How to read a down day
A few checks help when the market falls:
Size it. A fall of 1% or more came on 10.9% of days, about one in nine. A fall of 3% or more came on only 32 days in ten years.
Find the news. Check whether a jobs report, an inflation report or a Fed decision came out that day. Then check named news reports for what else happened.
Keep the year in view. April 2025 held the year's worst day. SPY (the S&P 500 exchange-traded fund, or ETF) still returned 17.7% in 2025, with dividends counted.
The stock market falls on news about interest rates, inflation, tariffs, politics, company results or shocks such as a pandemic. Those were the reasons reported for the S&P 500's worst day of each year from 2017 to 2026. Big rises often came within days of the biggest falls.
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