Impact on heart attack and stroke risk
A 2014 study in Open Heart documented a 25% increase in heart attacks on the Monday after the spring forward. A 2018 study found a 21% increase in adverse cardiovascular events on the Monday after the fall back.
The pattern is consistent enough that hospital systems in the US and Europe schedule extra cardiology staffing on the Monday after each clock change (Sleep Foundation, 2026).
Driving risk on the Sunday of the change
Pedestrian fatality data from the National Highway Traffic Safety Administration shows a small but persistent increase in the days following both clock changes.
The fall-back Sunday itself tends to see slightly more pedestrian fatalities as drivers adjust to darker evening commutes and disrupted circadian cues. School-zone and residential-area accidents are the largest contributors (NHTSA, 2025; Sleep Foundation, 2026).
Code and systems that handle DST
Most modern software libraries handle the fall-back correctly out of the box. The historical bug cases are:
Java's SimpleDateFormat and the legacy java.util.Date classes have produced off-by-one-hour errors in fall-back windows for years. Java 8+ `java.time.*` (LocalDateTime, ZonedDateTime, Instant) is correct. Migration is straightforward but not automatic.
POSIX strftime `%s` returns the local Unix timestamp interpreted without DST awareness. The fall-back hour repeats - so a `Date` constructed from `%s` can show 1:30 AM twice on November 1.
JavaScript Date objects store UTC milliseconds and compute local time at render. They handle DST correctly if the browser's timezone data is up to date. Embedded WebViews on older Android versions can show stale data and need OS-level timezone updates.
Cron jobs in the fall-back hour can fire twice or not at all depending on the implementation. Java Quartz, systemd timers, and Kubernetes CronJobs handle this differently - test your specific stack.
What changes for travel and meetings
International travel across the Atlantic or Pacific becomes one hour "easier" after the US falls back. A 9:00 AM EST meeting with a London colleague moves from 2:00 PM BST (summer) to 1:00 PM GMT (winter).
The IANA tzdata package, maintained by ICANN, tracks every DST rule change worldwide. Linux distributions ship tzdata updates that are applied via package manager. Windows applies DST changes via Windows Update. macOS uses Apple Software Update (NIST, 2026).
How to prepare
Three actions make the fall-back smoother.
First, adjust sleep schedules in the week before. Move bedtime 15 minutes earlier across the week leading up to November 1. The circadian shift is small but compounds with the clock change.
Second, update calendar entries that cross time zones. Conference calls scheduled for "2:00 AM" or any time during the fall-back hour should be confirmed - 1:00-2:00 AM local time repeats.
Third, review device clocks. Most modern phones update automatically. Laptops, smart home devices, and older appliances may need manual adjustment or an OS update (NIST, 2026).
Spring forward 2027
Daylight saving time begins again on Sunday, March 8, 2027 at 2:00 AM local time. Clocks spring forward one hour.
The spring forward trades one hour of morning sleep for one hour of evening daylight. The shift is felt hardest by school-age children and shift workers. Schools typically adjust schedules the prior week, shifting start times 15 minutes earlier across five school days to minimise the disruption.
The cycle has repeated under current law since the Uniform Time Act of 1966 (US Uniform Time Act, 2026).
Only a federal statute - the Sunshine Protection Act or a successor bill - would break the twice-yearly pattern. Until then, the spring 2027 forward and fall 2027 back are scheduled as written.
The four-month standard-time window - November through mid-March - is the longest period of solar alignment with standard time.
Solar noon (when the sun is highest in the sky) tracks closer to 12:00 PM on the clock during these months. For US Eastern time, solar noon lands around 11:50 AM to 12:00 PM during standard time, vs 12:50 PM to 1:00 PM during DST.
The transition to and from DST is the only time in the year when civil time and solar time diverge sharply.
Communities east of the solar meridian (roughly the eastern third of each time zone) experience solar noon even earlier - 11:40 AM or earlier during standard time. The misalignment is part of why some researchers advocate for permanent standard time.
Permanent standard time maximises morning light year-round. Researchers argue this improves sleep, mood, and public safety - the core rationale behind Bill C-289 in Canada and the contingent state laws in the US.
The pattern repeats under current law: spring forward second Sunday of March, fall back first Sunday of November (US Uniform Time Act, 2026).
Internal links
For the federal Sunshine Protection Act status and state-by-state map, see our states daylight saving laws 2026 post.
For the UK clocks-back change on October 25, 2026, see our UK clocks change October 2026 post.
For the Canada fall-back on November 1, 2026, see our Canada daylight saving ends November 2026 post.
Fazlur Rahman
