.calc-container {
max-width: 800px;
margin: 0 auto;
padding: 30px;
background: #f8f9fa;
border-radius: 12px;
border: 1px solid #e9ecef;
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
}
.calc-header {
text-align: center;
margin-bottom: 30px;
}
.calc-header h2 {
color: #2c3e50;
margin: 0;
font-size: 28px;
}
.calc-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.calc-col {
flex: 1;
min-width: 250px;
}
.calc-input-group {
margin-bottom: 15px;
}
.calc-label {
display: block;
font-weight: 600;
margin-bottom: 8px;
color: #495057;
}
.calc-input {
width: 100%;
padding: 12px;
border: 2px solid #dee2e6;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s;
}
.calc-input:focus {
border-color: #3498db;
outline: none;
}
.calc-select {
width: 100%;
padding: 12px;
border: 2px solid #dee2e6;
border-radius: 6px;
font-size: 16px;
background-color: white;
cursor: pointer;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #2c3e50;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #34495e;
}
.calc-results {
margin-top: 30px;
background: white;
padding: 25px;
border-radius: 8px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
align-items: center;
padding: 15px 0;
border-bottom: 1px solid #eee;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
color: #6c757d;
font-size: 16px;
}
.result-value {
font-weight: bold;
font-size: 24px;
color: #2c3e50;
}
.timeline-visual {
margin-top: 20px;
padding: 15px;
background: #eef2f5;
border-radius: 6px;
font-size: 14px;
color: #555;
border-left: 4px solid #3498db;
}
.error-msg {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
}
/* Article Styles */
.article-container {
max-width: 800px;
margin: 40px auto;
font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
}
.article-container h2 {
color: #2c3e50;
margin-top: 30px;
border-bottom: 2px solid #f1f1f1;
padding-bottom: 10px;
}
.article-container p {
margin-bottom: 15px;
}
.article-container ul {
margin-bottom: 20px;
padding-left: 20px;
}
.article-container li {
margin-bottom: 8px;
}
.info-box {
background-color: #e8f4f8;
border-left: 5px solid #3498db;
padding: 15px;
margin: 20px 0;
}
function calculateTimeline() {
// Clear previous errors and results
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('results');
errorDiv.style.display = 'none';
// Get Inputs
var startYearInput = document.getElementById('startYear').value;
var startEra = document.getElementById('startEra').value;
var endYearInput = document.getElementById('endYear').value;
var endEra = document.getElementById('endEra').value;
// Validation
if (startYearInput === "" || endYearInput === "" || isNaN(startYearInput) || isNaN(endYearInput)) {
errorDiv.innerHTML = "Please enter valid year numbers.";
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
var startYear = parseInt(startYearInput);
var endYear = parseInt(endYearInput);
if (startYear <= 0 || endYear 1 AD.
// Ensure logical order (Start is BC, End is AD) for positive result
if (isStartBC && !isEndBC) {
totalYears = startYear + endYear – 1;
formulaText = "Crossing from BC to AD requires adding the years and subtracting 1 (due to no Year 0): " + startYear + " + " + endYear + " – 1.";
} else {
// User put AD first then BC (Reverse chronological order)
totalYears = (startYear + endYear – 1) * -1; // Negative to indicate reverse
formulaText = "Calculated in reverse chronological order (AD to BC). Formula: (" + startYear + " + " + endYear + " – 1) * -1.";
}
}
// Handle negative result (if user put dates in wrong order within same era)
var isReverse = false;
if (totalYears < 0) {
totalYears = Math.abs(totalYears);
isReverse = true;
formulaText += "
The end date is earlier than the start date.";
}
// Calculate Generations (approx 25 years per generation)
var generations = (totalYears / 25).toFixed(1);
// Calculate Centuries
var centuries = (totalYears / 100).toFixed(2);
// Display Results
document.getElementById('totalYears').innerText = totalYears.toLocaleString() + " Years";
document.getElementById('totalCenturies').innerText = centuries;
document.getElementById('totalGenerations').innerText = generations;
document.getElementById('timelineExplanation').innerHTML = formulaText;
resultsDiv.style.display = 'block';
}
Understanding the BC and AD Date Calculator
Calculating the time difference between dates in history can be tricky, especially when crossing the boundary between BC (Before Christ) and AD (Anno Domini). Unlike modern mathematics where a zero separates positive and negative numbers, the historical calendar standard used by historians and archaeologists has no Year 0. This calculator helps you accurately determine the span between two historical years without getting tripped up by this common chronological quirk.
Key Concept: The Missing Year Zero
In the Gregorian and Julian calendars, the year 1 BC is immediately followed by the year 1 AD. There is no intervening "Year 0". This means that the span between January 1, 1 BC and January 1, 1 AD is exactly one year, not two.
How the Calculation Works
Depending on whether your dates fall within the same era or cross the BC/AD threshold, the math changes slightly. Here is the logic this tool uses:
1. Crossing from BC to AD
When calculating the duration between a date in the BC era and a date in the AD era, you simply add the two year numbers together and subtract one.
- Formula:
(BC Year + AD Year) - 1
- Example: From 10 BC to 10 AD.
- Math: 10 + 10 – 1 = 19 Years.
2. Both Dates in the Same Era (AD to AD)
If both dates are in the Common Era (AD or CE), the calculation is straightforward subtraction.
- Formula:
End Year - Start Year
- Example: From 1990 AD to 2023 AD.
- Math: 2023 – 1990 = 33 Years.
3. Both Dates in the Same Era (BC to BC)
Since BC counts backward (500 BC is earlier than 100 BC), you subtract the end year from the start year.
- Formula:
Start Year - End Year
- Example: From 500 BC to 200 BC.
- Math: 500 – 200 = 300 Years.
BC/AD vs. BCE/CE
You may often see the terms BCE (Before Common Era) and CE (Common Era). These are the secular equivalents of BC and AD.
Numerically, they function exactly the same. The year 500 BCE is the exact same year as 500 BC. This calculator allows you to select either notation, and the mathematical result will remain accurate.
Why is there no Year 0?
The Anno Domini dating system was devised in 525 AD by a monk named Dionysius Exiguus. At that time in Europe, the mathematical concept of zero was not widely used or understood in the same way it is today. Roman numerals, which were the standard, do not have a symbol for zero. Consequently, the calendar begins at Year 1.
This anomaly often causes "off-by-one" errors in historical calculations. For example, the 3rd Millennium officially began on January 1, 2001, not January 1, 2000, because the first millennium was years 1–1000.