Shabbat Timing and Candle Lighting Calculator

Introduction

This calculator is built for a very specific job: estimating the start and end timing markers that many Jewish households use for Shabbat preparation and conclusion. In everyday language, it answers three connected questions. First, when is sunset on the Friday that begins Shabbat at your location? Second, if your custom is to light candles a certain number of minutes before that sunset, what clock time does that produce? Third, when is sunset on the following Saturday, and what havdalah time do you get after adding your chosen waiting period?

That sounds straightforward, but the details matter. Shabbat times are not just a matter of looking up a city name and applying one universal rule. Two places on the same longitude can have different sunset behavior because of latitude. The same city changes dramatically across the year, with long summer evenings and early winter sunsets. Communities also vary. One family may use 18 minutes before sunset for candle lighting, another may use 30 or 40 minutes, and havdalah customs often differ even more. This calculator therefore separates the astronomy from the custom: it estimates sunset from location and date, then lets you apply the custom you actually follow.

It is also important to understand what the tool is and is not doing. It is an estimate based on simplified solar geometry rather than a full observatory-grade model with elevation, refraction refinements, or automatic timezone database lookups. That makes it fast and easy to audit. You can see which number came from astronomy and which number came from a community offset choice. For planning a meal, travel, reminders, or a family schedule, that transparency is often more useful than a black box.

If you compare the output with a synagogue bulletin or a communal calendar, you may notice small differences. That does not automatically mean the calculator is wrong. It may simply mean the community source uses a different havdalah convention, a slightly different astronomical model, a nearby reference city, or a daylight saving rule that differs from the UTC offset you entered. The safest way to use the calculator is as a planning tool and a consistency check: confirm your inputs, review the result, and compare it with the custom and authority you rely on in practice.

How to use

Start with the location fields. Latitude tells the calculator how far north or south you are, and longitude tells it how far east or west you are. Those two values are what allow the sunset estimate to respond to real geography rather than a generic average. For example, a Friday in New York and a Friday in Jerusalem occur on the same planet, but they do not share the same sunset or civil clock relationship. Entering the right coordinates is therefore the foundation of the whole result.

Next, enter the UTC offset that matches the local civil time you want the answer shown in. This field is deliberately manual because Shabbat planning is usually done in local clock time. If your area is on standard time, enter that offset. If your area is on daylight saving time, enter the daylight-saving offset instead. The field accepts half-hour offsets as well, which is helpful in places that do not use a whole number of hours from UTC.

Once the location and civil time are set, choose the offset before sunset for candle lighting and the offset after sunset for havdalah. These are the community-custom inputs. They do not change the sunset estimate itself; they change how the calculator converts sunset into an observance time. After you choose a Friday date and press calculate, review the Friday sunset, the derived candle-lighting time, the Saturday sunset, and the havdalah result together rather than reading only one number in isolation.

• Latitude: positive for north, negative for south. A wrong sign can place you in the wrong hemisphere and distort the season.
• Longitude: positive for east, negative for west. This affects the relation between solar noon and clock time.
• UTC offset: enter the local offset that matches the date you are planning for, including daylight saving time when applicable.
• Candle-lighting offset: minutes before Friday sunset, commonly 18 but sometimes different by local custom.
• Havdalah offset: minutes after Saturday sunset, often 42, 50, 60, or 72 depending on practice.
• Shabbat date: select the Friday that begins the Shabbat you want to plan.

After calculation, do a quick sanity check. In summer, longer day length often means later sunset. In winter, earlier sunset is normal. Candle lighting should always be earlier than Friday sunset by exactly the number of minutes you entered, and havdalah should be later than Saturday sunset by the offset you entered. If a result looks surprising, the first things to verify are the UTC offset, the coordinate signs, and whether you picked the correct Friday.

Formula

The calculator follows a simple chain. It first estimates the sun's seasonal declination and the equation of time for the selected date. Those values are then used with latitude and longitude to approximate solar noon and the hour angle at sunset. From that, the tool obtains an estimated local sunset time. Once sunset is known, the religious timing conventions are expressed as plain minute offsets relative to that sunset.

In direct form, the observance times are modeled as local sunset plus or minus a number of minutes. Friday candle lighting is earlier than Friday sunset, and Saturday havdalah is later than Saturday sunset:

Here, the offset values are in minutes, so the calculator divides by 60 to convert them into hours before adding or subtracting them from sunset. The Shabbat duration shown in the result panel is then the span from Friday candle lighting to Saturday havdalah, which is why it normally lands around twenty-five hours rather than around one hour. Friday sunset and Saturday sunset are computed separately because the sun's position changes from one day to the next.

The page already includes a general mathematical view of calculators as functions of several inputs. That still fits this tool well: the final timing result is a function of location, date, UTC offset, and custom offsets. Those general expressions are preserved below because they describe the structure of the calculation even though the specific astronomy is more specialized than a simple weighted sum.

In plain language, the calculator collects several inputs, transforms them into compatible units, applies the solar model, and then converts the answer into easy-to-read times. That is why units matter so much. Latitude and longitude are in degrees, UTC offset is in hours, and the observance customs are in minutes. If one of those units is entered incorrectly, the output can be off by much more than a rounding difference.

Example

Suppose you use the default New York-style demonstration inputs: latitude 40.7128, longitude -74.0060, a UTC offset of -5, candle lighting 18 minutes before sunset, and havdalah 42 minutes after sunset. After selecting a Friday date and running the calculator, imagine the Friday sunset estimate comes out as 17:31 and the Saturday sunset estimate comes out as 17:32. The derived observance times would then be easy to verify by hand: candle lighting would be 17:13 on Friday, and havdalah would be 18:14 on Saturday.

That example is useful because it shows what the offsets mean operationally. The astronomical part of the tool gives you sunset. The custom part shifts that sunset earlier or later. If you changed only the candle-lighting offset from 18 minutes to 30 minutes, the Friday candle-lighting result would move from 17:13 to 17:01, while the sunset itself would stay the same. If you changed only havdalah from 42 minutes to 72 minutes, the Saturday conclusion would move later, but Friday preparation time would not change. This makes the calculator handy for comparing community customs without changing the underlying location or date.

How to interpret the result

The result panel is designed to separate the core ingredients of the estimate. Friday sunset tells you the astronomical anchor for the start of Shabbat preparation. Candle-lighting time tells you the practical deadline after applying your chosen custom. Saturday sunset gives the second anchor, and havdalah converts that into a practical conclusion time. The solar day length and season are there as quick context checks. A very short winter day and an early sunset belong together; a very long summer day and a late sunset belong together.

If you are planning reminders, meals, travel, or hospitality, it often helps to read the result as a sequence rather than as isolated numbers: Friday sunset, Friday candle lighting, Saturday sunset, Saturday havdalah, then total Shabbat duration. That sequence mirrors how the calculator works internally and makes it easier to notice when an input seems inconsistent.

Limitations

No single online tool can encode every halachic custom or every local astronomical nuance. This calculator estimates sunset from coordinates and date, then applies straightforward offsets. That makes it clear and useful, but it also means you should understand the boundaries of the model before relying on it for an important schedule.

• Manual timezone entry: the UTC offset is whatever you type, so you must account for daylight saving time yourself.
• Community practice varies: candle-lighting and havdalah offsets are not universal. Your synagogue or rabbinic authority may follow a different standard.
• High latitudes: near the poles, there are dates when the sun does not rise or set in the usual way. The calculator will reject those edge cases because the simplified sunset model breaks down there.
• Simplified astronomy: elevation, local horizon, and more advanced atmospheric effects are not modeled here.
• Date interpretation: the form expects the Friday that begins Shabbat. Choosing another day changes the meaning of the result.

For routine planning, those limitations are usually manageable as long as you enter careful inputs and compare with trusted local guidance. For exact communal observance schedules, always defer to the authority or calendar your community follows. The calculator is best understood as a transparent estimator: it helps you reason about location, date, and offset choices in a way that is quick to audit and easy to explain to others.