Daylight Change Calculator
Compare daylight across a date range, see daily gains or losses and find the first date meeting your daylight-hours target for a chosen location.
Starts with an editable example. Replace the dates and rules with your own.
Your calculation
Ready when you are
Choose your dates.
Select your counting rules and calculate.
Calculation details
| Step | Value |
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How to use this calculator
Choose a location and up to 366 comparison dates. Enter a daylight target and whether you need at least or at most that amount.
Daylight is elapsed time with the Sun above the horizon within each local date. Daylight-saving transitions can change the length of that date. Polar days, polar nights and skipped local dates are handled explicitly.
A worked example
New York loses about 55 minutes 58 seconds of daylight from November 1 to November 30, 2026. November 13 is the first date in that range with at most ten hours.
Does the target search skip the first date?
No. If the first date already meets your target it is returned. The search reports the first qualifying date inside your entered range, not necessarily a seasonal crossing.
Which calendar and years are supported?
Use Gregorian dates from 1900 through 2100, with results in that range. Daily plans allow up to 366 dates; dark-sky searches allow 31 nights. Durations, capacities and policy rules are supplied by you. Astronomy uses the bundled Astronomy Engine, sea-level geometry and browser time-zone rules. Timed exports use UTC instants; date-only events do not assign a clock time. Copy, CSV and print include calculation assumptions. Nothing is booked or scheduled outside this page.
What happens to my dates?
Calculations run on your device. Saving a calculation is optional and keeps it in this browser. A setup link contains the dates and settings you entered; anyone with the link can read them. Use one tab per saved calculator. Clear saved data from Privacy & settings.