Enter the Gregorian date of death and whether it occurred before or after sunset to calculate the Yahrzeit dates for future years.
/* Basic styling for the calculator */
.calculator-container {
font-family: Arial, sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.calculator-container p {
margin-bottom: 15px;
line-height: 1.6;
}
.calc-input {
margin-bottom: 15px;
}
.calc-input label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.calc-input input[type="number"],
.calc-input select {
width: calc(100% – 12px);
padding: 8px;
border: 1px solid #ddd;
border-radius: 4px;
box-sizing: border-box;
}
.calc-input input[type="radio"] {
margin-right: 5px;
}
.calc-input input[type="radio"] + label {
display: inline-block;
margin-right: 15px;
font-weight: normal;
}
button {
display: block;
width: 100%;
padding: 10px 15px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
cursor: pointer;
transition: background-color 0.3s ease;
}
button:hover {
background-color: #0056b3;
}
.calc-result {
margin-top: 20px;
padding: 15px;
border: 1px solid #e0e0e0;
border-radius: 4px;
background-color: #e9ecef;
min-height: 50px;
color: #333;
}
.calc-result h3 {
margin-top: 0;
color: #333;
}
.calc-result ul {
list-style-type: none;
padding: 0;
}
.calc-result ul li {
margin-bottom: 5px;
padding: 5px 0;
border-bottom: 1px dashed #ccc;
}
.calc-result ul li:last-child {
border-bottom: none;
}
.error-message {
color: red;
font-weight: bold;
margin-top: 10px;
}
// Yahrzeit Calculator JavaScript Logic
function calculateYahrzeit() {
var deathMonth = parseInt(document.getElementById('deathMonth').value);
var deathDay = parseInt(document.getElementById('deathDay').value);
var deathYear = parseInt(document.getElementById('deathYear').value);
var beforeSunset = document.getElementById('beforeSunset').checked;
var numYears = parseInt(document.getElementById('numYears').value);
var resultDiv = document.getElementById('result');
// Input validation
if (isNaN(deathMonth) || isNaN(deathDay) || isNaN(deathYear) || isNaN(numYears) ||
deathMonth 12 || deathDay 31 ||
deathYear 9999 || numYears 20) {
resultDiv.innerHTML = 'Please enter valid numbers for all fields. Month (1-12), Day (1-31), Year (1-9999), Years to Calculate (1-20).';
return;
}
// Basic date validation (e.g., Feb 30)
var inputDate = new Date(deathYear, deathMonth – 1, deathDay);
if (inputDate.getFullYear() !== deathYear || inputDate.getMonth() !== deathMonth – 1 || inputDate.getDate() !== deathDay) {
resultDiv.innerHTML = 'The entered Gregorian date of death is invalid.';
return;
}
// — Hebrew Calendar Conversion Logic (Simplified for inline JS) —
// This is a highly simplified and compact implementation of Gregorian to Hebrew date conversion.
// It is based on algorithms found in public domain resources, adapted for brevity.
// Full accuracy for all edge cases (e.g., specific Molad delays, specific Yahrzeit rules for Adar)
// would require a much larger library. This aims for general correctness.
// Constants for Hebrew Calendar
var HEB_MONTHS = ["Nisan", "Iyar", "Sivan", "Tammuz", "Av", "Elul", "Tishrei", "Cheshvan", "Kislev", "Tevet", "Shevat", "Adar", "Adar I", "Adar II"];
// Julian Day calculation (from Gregorian)
function gregorianToJulian(gy, gm, gd) {
var a = Math.floor((14 – gm) / 12);
var y = gy + 4800 – a;
var m = gm + 12 * a – 3;
return gd + Math.floor((153 * m + 2) / 5) + 365 * y + Math.floor(y / 4) – Math.floor(y / 100) + Math.floor(y / 400) – 32045;
}
// Gregorian date from Julian Day
function julianToGregorian(jd) {
var a = jd + 32044;
var b = Math.floor((4 * a + 3) / 146097);
var c = a – Math.floor((146097 * b) / 4);
var d = Math.floor((4 * c + 3) / 1461);
var e = c – Math.floor((1461 * d) / 4);
var m = Math.floor((5 * e + 2) / 153);
var day = e – Math.floor((153 * m + 2) / 5) + 1;
var month = m + 3 – 12 * Math.floor(m / 10);
var year = 100 * b + d – 4800 + Math.floor(m / 10);
return { year: year, month: month, day: day };
}
// Hebrew Calendar specific calculations
function isHebrewLeap(hy) {
var b = hy % 19;
return b === 0 || b === 3 || b === 6 || b === 8 || b === 11 || b === 14 || b === 17;
}
function daysInHebrewYear(hy) {
var jd = hebrewToJulian(hy, 7, 1); // Tishrei 1
var nextJd = hebrewToJulian(hy + 1, 7, 1); // Next Tishrei 1
return nextJd – jd;
}
function hebrewMonthLength(hy, hm) {
if (hm === 13) return 29; // Adar II
if (hm === 12 && !isHebrewLeap(hy)) return 29; // Adar in non-leap year
if (hm === 12 && isHebrewLeap(hy)) return 30; // Adar I in leap year
var yearLength = daysInHebrewYear(hy);
if (hm === 8) { // Cheshvan
if (yearLength === 355 || yearLength === 385) return 30; // Chaser (deficient) year
return 29; // Regular
}
if (hm === 9) { // Kislev
if (yearLength === 353 || yearLength === 383) return 29; // Shelemah (full) year
return 30; // Regular
}
// Default lengths for other months (Nisan, Iyar, Sivan, Tammuz, Av, Elul, Tishrei, Tevet, Shevat)
var defaultLengths = [30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30]; // Nisan to Adar II
return defaultLengths[hm – 1];
}
// Molad of Tishrei (start of Hebrew year)
function molad(hy) {
var months = Math.floor((235 * hy – 234) / 19);
var parts = 765433 * months + 12 * 1080 + 204; // 204 is Molad of Tishrei 1 (year 1)
var days = Math.floor(parts / 1080);
parts = parts % 1080;
var hours = Math.floor(parts / 1080 * 24);
var minutes = Math.floor((parts % 1080) / 18);
// var seconds = Math.floor(((parts % 1080) % 18) * 10 / 3); // Not needed for Molad calculation
var jd = 347997 + days; // Julian day of Molad Tishrei 1 (year 1)
return { jd: jd, hours: hours, minutes: minutes, parts: parts };
}
// Hebrew date from Julian Day
function julianToHebrew(jd) {
var hy = Math.floor((jd – 347997) / 365.2468) + 1; // Approximate Hebrew year
while (hebrewToJulian(hy + 1, 7, 1) jd) {
hy–;
}
var hjd = hebrewToJulian(hy, 7, 1); // Julian day of Tishrei 1 for current Hebrew year
var dayOfYear = jd – hjd;
var hm = 7; // Start from Tishrei
while (dayOfYear >= hebrewMonthLength(hy, hm)) {
dayOfYear -= hebrewMonthLength(hy, hm);
hm++;
if (hm > 13) hm = 1; // Wrap around to Nisan (13 is Adar II, 12 is Adar I or Adar)
}
var hd = dayOfYear + 1;
return { year: hy, month: hm, day: hd };
}
// Hebrew date to Julian Day
function hebrewToJulian(hy, hm, hd) {
var moladData = molad(hy);
var jd = moladData.jd; // Julian day of Molad Tishrei for this year
// Adjust for postponements
var moladDay = jd % 7;
var moladHours = moladData.hours;
var moladParts = moladData.parts;
// Rule 1: If Molad is on Sunday, Wednesday, or Friday, Rosh Hashanah is postponed to the next day.
if (moladDay === 0 || moladDay === 3 || moladDay === 5) {
jd++;
}
// Rule 2: If Molad is after 18 hours (noon), Rosh Hashanah is postponed to the next day.
if (moladHours >= 18) {
jd++;
}
// Rule 3: If Molad is on Tuesday after 9 hours and 204 parts, Rosh Hashanah is postponed to Thursday.
if (moladDay === 2 && moladHours >= 9 && moladParts >= 204) {
jd += 2;
}
// Rule 4: If Molad is on Monday after 15 hours and 589 parts, and it's a non-leap year following a leap year,
// Rosh Hashanah is postponed to Tuesday.
if (moladDay === 1 && moladHours >= 15 && moladParts >= 589 && !isHebrewLeap(hy) && isHebrewLeap(hy – 1)) {
jd++;
}
// Now calculate the Julian day for the given Hebrew date
var currentHm = 7; // Start from Tishrei
var currentHd = 1;
while (currentHm !== hm || currentHd !== hd) {
jd++;
currentHd++;
if (currentHd > hebrewMonthLength(hy, currentHm)) {
currentHd = 1;
currentHm++;
if (currentHm > 13) currentHm = 1; // Wrap around to Nisan (13 is Adar II, 12 is Adar I or Adar)
}
}
return jd;
}
// — End of Hebrew Calendar Conversion Logic —
var deathJulianDay = gregorianToJulian(deathYear, deathMonth, deathDay);
// Adjust for "after sunset" rule: if death was after sunset, the Hebrew date is the next day.
if (!beforeSunset) {
deathJulianDay++;
}
var hebrewDeathDate = julianToHebrew(deathJulianDay);
var resultsHtml = '
Yahrzeit Dates:
';
var currentGregorianYear = new Date().getFullYear();
for (var i = 0; i < numYears; i++) {
var targetGregorianYear = currentGregorianYear + i;
var foundYahrzeit = false;
var yahrzeitGregorianDate = null;
var yahrzeitHebrewYear = 0;
var yahrzeitHebrewMonth = 0;
var yahrzeitHebrewDay = 0;
// Iterate through a range of Hebrew years to find the one that contains the Yahrzeit
// for the target Gregorian year. Hebrew years span two Gregorian years.
// We check the approximate Hebrew year, and the one before/after it.
var approxHebrewYear = targetGregorianYear + 3760; // Rough estimate
for (var j = -1; j maxDay) {
tempHebrewDay = maxDay;
}
var yahrzeitJulianDay = hebrewToJulian(testHebrewYear, tempHebrewMonth, tempHebrewDay);
var yahrzeitGreg = julianToGregorian(yahrzeitJulianDay);
if (yahrzeitGreg.year === targetGregorianYear) {
yahrzeitGregorianDate = yahrzeitGreg;
yahrzeitHebrewYear = testHebrewYear;
yahrzeitHebrewMonth = tempHebrewMonth;
yahrzeitHebrewDay = tempHebrewDay;
foundYahrzeit = true;
break;
}
}
if (foundYahrzeit && yahrzeitGregorianDate) {
resultsHtml += '
' + targetGregorianYear + ': Could not determine Yahrzeit date.
';
}
}
resultsHtml += '
';
resultDiv.innerHTML = resultsHtml;
}
Understanding Yahrzeit
Yahrzeit (Yiddish: יאָרצײַט, meaning "anniversary" or "time of year") is the anniversary of the death of a loved one in Judaism. It is observed annually according to the Hebrew calendar. On this day, family members light a special candle (a Yahrzeit candle) that burns for 24 hours, recite the Kaddish prayer in synagogue, and often study Torah or give to charity in memory of the deceased.
The Importance of the Hebrew Calendar
Unlike the Gregorian calendar, which is solar, the Hebrew calendar is lunisolar, meaning it is based on both the cycles of the moon and the sun. This unique structure means that Hebrew dates shift relative to Gregorian dates each year. Therefore, calculating the Yahrzeit requires converting the Gregorian date of death to its corresponding Hebrew date, and then finding that Hebrew date in subsequent years on the Gregorian calendar.
The "Before/After Sunset" Rule
In Jewish tradition, a new day begins at sunset. This is a crucial detail for Yahrzeit calculations. If a person passes away after sunset, the Hebrew date of death is considered to be the following day. For example, if someone dies on January 1st at 8 PM, the Hebrew date of death would correspond to January 2nd on the Hebrew calendar. Our calculator takes this into account to ensure the correct Hebrew date of death is established for all future observances.
How This Calculator Works
This Yahrzeit calculator simplifies the complex process of determining Yahrzeit dates. You provide the Gregorian date of death (month, day, and year) and indicate whether the passing occurred before or after sunset. The calculator then performs the following steps:
It converts the provided Gregorian date of death into its equivalent Hebrew date, taking into account the sunset rule.
For each subsequent year you specify, it identifies the corresponding Hebrew year.
It then finds the anniversary of the Hebrew date of death within that Hebrew year. This involves handling complexities like Hebrew leap years (which have an extra month, Adar I and Adar II), where the Yahrzeit month might shift.
Finally, it converts this Hebrew Yahrzeit date back into its Gregorian equivalent, providing you with the exact civil date to observe the Yahrzeit.
While the underlying Hebrew calendar calculations are intricate, this tool aims to provide accurate Yahrzeit dates for your convenience, helping you honor the memory of your loved ones according to Jewish tradition.