function calculateBloodQuantum() {
var motherVal = parseFloat(document.getElementById('motherQuantum').value);
var fatherVal = parseFloat(document.getElementById('fatherQuantum').value);
if (isNaN(motherVal) || isNaN(fatherVal)) {
alert("Please select valid options for both parents.");
return;
}
// Formula: (Mother + Father) / 2
var childDecimal = (motherVal + fatherVal) / 2;
var percentage = (childDecimal * 100).toFixed(3) + "%";
// Convert decimal to fraction
var fractionText = "0";
if (childDecimal > 0) {
var tolerance = 1.0E-6;
var h1 = 1; var h2 = 0;
var k1 = 0; var k2 = 1;
var b = childDecimal;
do {
var a = Math.floor(b);
var aux = h1; h1 = a * h1 + h2; h2 = aux;
aux = k1; k1 = a * k1 + k2; k2 = aux;
b = 1 / (b – a);
} while (Math.abs(childDecimal – h1 / k1) > childDecimal * tolerance);
// Adjust for standard blood quantum denominators (powers of 2)
// While the continuous fraction is accurate, BQ is usually expressed in powers of 2.
// Let's force a power of 2 denominator check up to 256 for display cleanliness
var bestNum = 0;
var bestDenom = 1;
var minError = 1;
var denoms = [1, 2, 4, 8, 16, 32, 64, 128, 256];
for (var i = 0; i < denoms.length; i++) {
var d = denoms[i];
var n = Math.round(childDecimal * d);
var val = n / d;
var error = Math.abs(val – childDecimal);
if (error < 0.000001) {
bestNum = n;
bestDenom = d;
break;
}
}
if (bestNum === bestDenom) {
fractionText = "Full Blood (4/4)";
} else {
fractionText = bestNum + "/" + bestDenom;
}
} else {
fractionText = "None (0)";
}
var resultDiv = document.getElementById('result');
resultDiv.style.display = 'block';
resultDiv.innerHTML =
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This Blood Quantum Calculator is designed to help individuals determine the degree of Native American ancestry they possess based on the documented blood quantum of their parents. The concept of "Blood Quantum" is a legal and political metric used by many Native American tribes and government agencies, such as the Bureau of Indian Affairs (BIA) in the United States, to define tribal membership eligibility.
The result is typically expressed as a fraction (e.g., 1/4, 1/8) or a percentage. It is important to note that blood quantum is distinct from DNA ethnicity estimates; it is a calculation based on traceable lineage to specific ancestors listed on base rolls, such as the Dawes Rolls.
How the Calculation Works
The mathematics behind blood quantum are relatively straightforward. The degree of Indian blood an individual possesses is equal to one-half of the sum of the parents' degrees.
In this scenario, the child would possess a blood quantum of 3/8.
Understanding CDIB and Tribal Enrollment
The Certificate of Degree of Indian Blood (CDIB) is an official U.S. government document that certifies an individual possesses a specific degree of Native American blood of a federally recognized Indian tribe, band, nation, pueblo, village, or community. To obtain a CDIB, you must provide supporting legal documents such as birth certificates showing your relationship to an ancestor whose name appears on a specific base roll.
Minimum Requirements
Tribes set their own enrollment criteria, and these requirements vary significantly widely:
1/4 (25%): A common minimum requirement for many tribes (e.g., Navajo Nation).
1/8 or 1/16: Required by other tribes (e.g., some Apache or Chippewa bands).
Lineal Descent: Some tribes do not require a specific minimum blood quantum, only proof of direct descent from an original enrollee (e.g., Cherokee Nation).
Why is Blood Quantum Controversial?
While this calculator provides the mathematical result used for legal processing, the concept of blood quantum is highly debated. Critics argue that it was originally imposed by the federal government to limit tribal citizenship and treaty obligations. Over time, as members marry outside the tribe, the mathematical blood quantum of descendants naturally decreases, leading to what some call "statistical genocide."
Conversely, proponents argue that it helps preserve tribal resources and cultural integrity by ensuring members have a close biological tie to the community. Regardless of the political debate, the mathematical calculation remains the standard for processing CDIB applications and tribal memberships today.
Disclaimer: This calculator is for educational and estimation purposes only. It does not constitute legal proof of heritage. Official determination of blood quantum is handled by individual tribal enrollment offices and the Bureau of Indian Affairs.