The Hebrew calendar, also known as the Jewish calendar, is a lunisolar calendar used predominantly for Jewish religious observances. Unlike the Gregorian calendar, which is purely solar, the Hebrew calendar tracks both the moon's phases and the solar year. This unique system means that your Hebrew birthday falls on a different Gregorian date each year, though it always corresponds to the same Hebrew date.
The Lunisolar System
The Hebrew calendar's months are based on the cycles of the moon, with each new month beginning with the appearance of the new moon (Rosh Chodesh). A standard lunar year is about 354 days long, which is roughly 11 days shorter than a solar year. To keep the calendar aligned with the seasons (which are tied to the solar year, important for agricultural festivals like Passover and Sukkot), a leap month (Adar I) is added seven times over a 19-year cycle. This ensures that holidays like Passover always fall in the spring.
Why is Your Hebrew Birthday Important?
For many, celebrating one's Hebrew birthday holds special spiritual significance. It's considered a personal Rosh Hashanah (New Year), a time for reflection, spiritual growth, and setting new intentions for the year ahead. Some traditions include studying a new chapter of Psalms, giving extra charity, or making a special blessing on this day.
How the Hebrew Birthday Calculator Works
This calculator helps you discover your Hebrew birth date based on your Gregorian birth date. It then determines your next upcoming Hebrew birthday according to the Gregorian calendar and tells you how many days are left until that special day. The conversion between the Gregorian and Hebrew calendars is complex, involving intricate astronomical calculations and specific rules for adjusting month lengths and leap years to maintain alignment with both lunar and solar cycles.
Simply enter your birth day, month, and year in the fields below, and the calculator will do the rest!
Hebrew Birthday Calculator
January
February
March
April
May
June
July
August
September
October
November
December
Your Hebrew Birthday Details:
Your Hebrew Birth Date:
Next Hebrew Birthday (Gregorian):
Days Until Next Hebrew Birthday:
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border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
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margin: 20px auto;
font-family: Arial, sans-serif;
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.calculator-container h3 {
text-align: center;
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.calculator-input-group input[type="number"],
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padding: 10px;
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border-radius: 4px;
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.calculator-container button {
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// — Hebrew Calendar Constants and Helper Functions (Reingold & Dershowitz adapted) —
// JDN of 1 Tishrei, 1 AM, year 1 (Gregorian 6 October 3761 BCE)
var HEBREW_EPOCH = 347997;
var HEBREW_MONTH_NAMES = [
"", // 0-indexed, so 0 is empty
"Nisan", "Iyar", "Sivan", "Tammuz", "Av", "Elul",
"Tishrei", "Cheshvan", "Kislev", "Tevet", "Shevat", "Adar", "Adar II"
];
// Helper function to check if a Hebrew year is a leap year
function isHebrewLeap(hYear) {
var b = hYear * 7 + 1;
return (b % 19 = 1080 * 18) {
jd++;
}
// Rule 3: If molad of a non-leap year is on Tuesday, and it's after 9 hours and 204 parts,
// Rosh Hashanah is postponed to Thursday.
if (!isHebrewLeap(hYear) && moladDay % 7 === 2 && moladParts >= 1080 * 9 + 204) { // 2=Tue
jd += 2; // Postpone to Thursday
}
// Rule 4: If molad of a leap year is on Monday, and it's after 15 hours and 589 parts,
// Rosh Hashanah is postponed to Tuesday.
if (isHebrewLeap(hYear – 1) && moladDay % 7 === 1 && moladParts >= 1080 * 15 + 589) { // 1=Mon
jd++;
}
// Re-check Rule 1 after postponements
if (jd % 7 === 0 || jd % 7 === 3 || jd % 7 === 5) {
jd++;
}
return jd;
}
// Helper function to calculate the number of days in a Hebrew year
function hebrewCalendarYearLength(hYear) {
return hebrewCalendarNewYear(hYear + 1) – hebrewCalendarNewYear(hYear);
}
// Helper function to get the number of days in a specific Hebrew month for a specific year
function hebrewMonthDays(hMonth, hYear) {
var yearLength = hebrewCalendarYearLength(hYear);
var isLeap = isHebrewLeap(hYear);
// Standard month lengths
var monthLengths = [
0, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29, 30, 29 // Nisan to Adar II
];
if (isLeap) {
monthLengths[12] = 29; // Adar II
monthLengths[11] = 30; // Adar I
} else {
monthLengths[11] = 30; // Adar
}
// Adjust Cheshvan (8) and Kislev (9) based on year length
if (yearLength === 353 || yearLength === 383) { // Deficient year
monthLengths[8] = 29; // Cheshvan
monthLengths[9] = 29; // Kislev
} else if (yearLength === 355 || yearLength === 385) { // Complete year
monthLengths[8] = 30; // Cheshvan
monthLengths[9] = 30; // Kislev
} else { // Regular year (354 or 384)
monthLengths[8] = 29; // Cheshvan
monthLengths[9] = 30; // Kislev
}
return monthLengths[hMonth];
}
// — Gregorian to Julian Day Number (JDN) —
function gregorianToJDN(year, month, day) {
var a = Math.floor((14 – month) / 12);
var y = year + 4800 – a;
var m = month + 12 * a – 3;
return day + Math.floor((153 * m + 2) / 5) + 365 * y + Math.floor(y / 4) – Math.floor(y / 100) + Math.floor(y / 400) – 32045;
}
// — JDN to Gregorian Date —
function jdnToGregorian(jdn) {
var a = jdn + 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 = d + 100 * b – 4800 + Math.floor(m / 10);
return { year: year, month: month, day: day };
}
// — Hebrew to JDN —
function hebrewToJDN(hYear, hMonth, hDay) {
var jd = hebrewCalendarNewYear(hYear); // JDN of Rosh Hashanah for hYear
// Add days for preceding months
// Hebrew year starts with Tishrei (month 7)
for (var m = 7; m <= 12; m++) { // Tishrei (7) to Adar II (12)
if (m === hMonth) break;
jd += hebrewMonthDays(m, hYear);
}
for (var m = 1; m < 7; m++) { // Nisan (1) to Elul (6)
if (m === hMonth) break;
jd += hebrewMonthDays(m, hYear);
}
// Add days for the current month
jd += hDay – 1;
return jd;
}
// — JDN to Hebrew Date —
function jdnToHebrew(jdn) {
var hYear = Math.floor((jdn – HEBREW_EPOCH) / 365.2425) + 1; // Approximate Hebrew year
while (jdn = hebrewCalendarNewYear(hYear + 1)) {
hYear++;
}
var dayInYear = jdn – hebrewCalendarNewYear(hYear);
var hMonth = 0;
var hDay = 0;
// Iterate through months to find the correct month and day
// Start from Tishrei (7) as it's the start of the Hebrew year for calculation purposes
for (var m = 7; m <= 12; m++) {
var daysInMonth = hebrewMonthDays(m, hYear);
if (dayInYear < daysInMonth) {
hMonth = m;
hDay = dayInYear + 1;
break;
}
dayInYear -= daysInMonth;
}
if (hMonth === 0) { // If not found in Tishrei-Adar II, check Nisan-Elul
for (var m = 1; m < 7; m++) {
var daysInMonth = hebrewMonthDays(m, hYear);
if (dayInYear < daysInMonth) {
hMonth = m;
hDay = dayInYear + 1;
break;
}
dayInYear -= daysInMonth;
}
}
return { year: hYear, month: hMonth, day: hDay };
}
// — Main Calculator Logic —
function calculateHebrewBirthday() {
var gregorianDay = parseInt(document.getElementById("gregorianDay").value);
var gregorianMonth = parseInt(document.getElementById("gregorianMonth").value);
var gregorianYear = parseInt(document.getElementById("gregorianYear").value);
var errorMessages = document.getElementById("errorMessages");
errorMessages.innerHTML = ""; // Clear previous errors
// Input validation
if (isNaN(gregorianDay) || isNaN(gregorianMonth) || isNaN(gregorianYear) ||
gregorianDay 31 ||
gregorianMonth 12 ||
gregorianYear 2100) {
errorMessages.innerHTML = "Please enter valid Gregorian birth date (Day: 1-31, Month: 1-12, Year: 1900-2100).";
return;
}
// Validate if the date actually exists (e.g., no Feb 30)
var testDate = new Date(gregorianYear, gregorianMonth – 1, gregorianDay);
if (testDate.getFullYear() !== gregorianYear ||
testDate.getMonth() !== gregorianMonth – 1 ||
testDate.getDate() !== gregorianDay) {
errorMessages.innerHTML = "The Gregorian date entered is not a valid date.";
return;
}
// 1. Convert Gregorian Birth Date to Hebrew Birth Date
var jdnBirth = gregorianToJDN(gregorianYear, gregorianMonth, gregorianDay);
var hebrewBirth = jdnToHebrew(jdnBirth);
var hebrewMonthName = HEBREW_MONTH_NAMES[hebrewBirth.month];
// Adjust Adar name for display
if (hebrewBirth.month === 11 && isHebrewLeap(hebrewBirth.year)) {
hebrewMonthName = "Adar I";
} else if (hebrewBirth.month === 12 && isHebrewLeap(hebrewBirth.year)) {
hebrewMonthName = "Adar II";
} else if (hebrewBirth.month === 11 && !isHebrewLeap(hebrewBirth.year)) { // Adar is month 11 in non-leap year
hebrewMonthName = "Adar";
}
document.getElementById("hebrewBirthDate").innerHTML = hebrewBirth.day + " " + hebrewMonthName + ", " + hebrewBirth.year;
// 2. Find the Next Hebrew Birthday (Gregorian Date)
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today to start of day
var currentGregorianYear = today.getFullYear();
var nextHebrewBirthdayJDN;
var nextHebrewBirthdayGregorianDate;
// Get the Hebrew year corresponding to the current Gregorian year
var currentHebrewYear = jdnToHebrew(gregorianToJDN(currentGregorianYear, 1, 1)).year;
var targetHebrewMonth = hebrewBirth.month;
var targetHebrewDay = hebrewBirth.day;
// Special handling for Adar I/II birthdays
var originalBirthIsLeap = isHebrewLeap(hebrewBirth.year);
// If original birth was Adar I (month 11) in a leap year
if (hebrewBirth.month === 11 && originalBirthIsLeap) {
if (isHebrewLeap(currentHebrewYear)) {
targetHebrewMonth = 11; // Celebrate in Adar I
} else {
targetHebrewMonth = 11; // Celebrate in Adar (month 11)
}
}
// If original birth was Adar II (month 12) in a leap year
else if (hebrewBirth.month === 12 && originalBirthIsLeap) {
if (isHebrewLeap(currentHebrewYear)) {
targetHebrewMonth = 12; // Celebrate in Adar II
} else {
targetHebrewMonth = 11; // Celebrate in Adar (month 11)
}
}
// If original birth was Adar (month 11) in a non-leap year
else if (hebrewBirth.month === 11 && !originalBirthIsLeap) {
if (isHebrewLeap(currentHebrewYear)) {
targetHebrewMonth = 12; // Celebrate in Adar II
} else {
targetHebrewMonth = 11; // Celebrate in Adar
}
}
nextHebrewBirthdayJDN = hebrewToJDN(currentHebrewYear, targetHebrewMonth, targetHebrewDay);
nextHebrewBirthdayGregorianDate = jdnToGregorian(nextHebrewBirthdayJDN);
var nextBirthdayDate = new Date(nextHebrewBirthdayGregorianDate.year, nextHebrewBirthdayGregorianDate.month – 1, nextHebrewBirthdayGregorianDate.day);
// If the calculated birthday for the current Hebrew year has already passed, calculate for the next Hebrew year
if (nextBirthdayDate < today) {
currentHebrewYear++;
// Re-evaluate Adar I/II for the *next* Hebrew year
var nextYearIsLeap = isHebrewLeap(currentHebrewYear);
if (hebrewBirth.month === 11 && originalBirthIsLeap) { // Original was Adar I
if (nextYearIsLeap) {
targetHebrewMonth = 11; // Celebrate in Adar I
} else {
targetHebrewMonth = 11; // Celebrate in Adar
}
} else if (hebrewBirth.month === 12 && originalBirthIsLeap) { // Original was Adar II
if (nextYearIsLeap) {
targetHebrewMonth = 12; // Celebrate in Adar II
} else {
targetHebrewMonth = 11; // Celebrate in Adar
}
} else if (hebrewBirth.month === 11 && !originalBirthIsLeap) { // Original was Adar
if (nextYearIsLeap) {
targetHebrewMonth = 12; // Celebrate in Adar II
} else {
targetHebrewMonth = 11; // Celebrate in Adar
}
} else {
targetHebrewMonth = hebrewBirth.month; // For non-Adar months, month number is consistent
}
nextHebrewBirthdayJDN = hebrewToJDN(currentHebrewYear, targetHebrewMonth, targetHebrewDay);
nextHebrewBirthdayGregorianDate = jdnToGregorian(nextHebrewBirthdayJDN);
nextBirthdayDate = new Date(nextHebrewBirthdayGregorianDate.year, nextHebrewBirthdayGregorianDate.month – 1, nextHebrewBirthdayGregorianDate.day);
}
var options = { year: 'numeric', month: 'long', day: 'numeric' };
document.getElementById("nextHebrewBirthdayGregorian").innerHTML = nextBirthdayDate.toLocaleDateString('en-US', options);
// 3. Calculate Days Until Next Hebrew Birthday
var timeDiff = nextBirthdayDate.getTime() – today.getTime();
var daysUntil = Math.ceil(timeDiff / (1000 * 60 * 60 * 24));
document.getElementById("daysUntilNextBirthday").innerHTML = daysUntil;
}
// Set default values for demonstration
document.addEventListener('DOMContentLoaded', function() {
document.getElementById('gregorianDay').value = 15;
document.getElementById('gregorianMonth').value = 4; // April
document.getElementById('gregorianYear').value = 1990;
calculateHebrewBirthday(); // Calculate on load with defaults
});