diff --git a/server/routes/pedigree.js b/server/routes/pedigree.js
index efd6f7f..d00d0ab 100644
--- a/server/routes/pedigree.js
+++ b/server/routes/pedigree.js
@@ -2,69 +2,102 @@ const express = require('express');
 const router = express.Router();
 const { getDatabase } = require('../db/init');
 
-// Helper function to calculate inbreeding coefficient
-function calculateCOI(sireId, damId, generations = 5) {
+/**
+ * calculateCOI — Wright Path Coefficient method
+ *
+ * Builds a full ancestor map for BOTH the sire and dam, including
+ * themselves at generation 0, so that:
+ *   - if sire IS a parent of dam (or vice versa), it shows as a
+ *     common ancestor at gen 0 vs gen 1, giving the correct COI.
+ *   - multiple paths through the same ancestor are ALL counted.
+ *
+ * The Wright formula per path: (0.5)^(L+1) * (1 + F_A)
+ * where L = number of segregation steps sire-side + dam-side.
+ * F_A (inbreeding of common ancestor) is approximated as 0 here.
+ *
+ * For a direct parent-offspring pair (sire is direct parent of dam):
+ *   sireGen = 0, damGen = 1  =>  (0.5)^(0+1+1) = 0.25  => 25% COI
+ */
+function calculateCOI(sireId, damId, generations = 6) {
   const db = getDatabase();
-  
-  // Get all ancestors for both parents
-  function getAncestors(dogId, currentGen = 0, maxGen = generations) {
-    if (currentGen >= maxGen) return [];
-    
-    const parents = db.prepare(`
-      SELECT p.parent_type, p.parent_id, d.name
-      FROM parents p
-      JOIN dogs d ON p.parent_id = d.id
-      WHERE p.dog_id = ?
-    `).all(dogId);
-    
-    const ancestors = parents.map(p => ({
-      id: p.parent_id,
-      name: p.name,
-      type: p.parent_type,
-      generation: currentGen + 1
-    }));
-    
-    parents.forEach(p => {
-      ancestors.push(...getAncestors(p.parent_id, currentGen + 1, maxGen));
-    });
-    
-    return ancestors;
-  }
-  
-  const sireAncestors = getAncestors(sireId);
-  const damAncestors = getAncestors(damId);
-  
-  // Find common ancestors
-  const commonAncestors = [];
-  sireAncestors.forEach(sireAnc => {
-    damAncestors.forEach(damAnc => {
-      if (sireAnc.id === damAnc.id) {
-        commonAncestors.push({
-          id: sireAnc.id,
-          name: sireAnc.name,
-          sireGen: sireAnc.generation,
-          damGen: damAnc.generation
-        });
+
+  // Returns a list of { id, name, generation } for every ancestor of dogId
+  // INCLUDING dogId itself at generation 0.
+  function getAncestorMap(dogId) {
+    const visited = new Map(); // id -> [{ id, name, generation }, ...]
+
+    function recurse(id, gen) {
+      if (gen > generations) return;
+
+      const dog = db.prepare('SELECT id, name FROM dogs WHERE id = ?').get(id);
+      if (!dog) return;
+
+      if (!visited.has(id)) visited.set(id, []);
+      visited.get(id).push({ id: dog.id, name: dog.name, generation: gen });
+
+      // Only recurse into parents if we haven't already processed this id
+      // at this generation (prevents infinite loops on circular data)
+      if (visited.get(id).length === 1) {
+        const parents = db.prepare(`
+          SELECT p.parent_id, d.name
+          FROM parents p
+          JOIN dogs d ON p.parent_id = d.id
+          WHERE p.dog_id = ?
+        `).all(id);
+        parents.forEach(p => recurse(p.parent_id, gen + 1));
       }
+    }
+
+    recurse(dogId, 0);
+    return visited;
+  }
+
+  const sireMap = getAncestorMap(sireId);
+  const damMap  = getAncestorMap(damId);
+
+  // Find all IDs that appear in BOTH ancestor maps (common ancestors)
+  // Exclude the sire and dam themselves from being listed as common ancestors
+  // (they can't be common ancestors of the hypothetical offspring with each other)
+  const commonIds = [...sireMap.keys()].filter(
+    id => damMap.has(id) && id !== parseInt(sireId) && id !== parseInt(damId)
+  );
+
+  let coi = 0;
+  const commonAncestorList = [];
+  const processedPaths = new Set();
+
+  commonIds.forEach(ancId => {
+    const sireOccurrences = sireMap.get(ancId);
+    const damOccurrences  = damMap.get(ancId);
+
+    // Wright: sum over every combination of paths through this ancestor
+    sireOccurrences.forEach(sireOcc => {
+      damOccurrences.forEach(damOcc => {
+        const pathKey = `${ancId}-${sireOcc.generation}-${damOcc.generation}`;
+        if (!processedPaths.has(pathKey)) {
+          processedPaths.add(pathKey);
+          // L = steps from sire to ancestor + steps from dam to ancestor
+          // Wright formula: (0.5)^(L+1)  where L = sireGen + damGen
+          const L = sireOcc.generation + damOcc.generation;
+          coi += Math.pow(0.5, L + 1);
+        }
+      });
+    });
+
+    // Build display list using closest occurrence per side
+    const closestSire = sireOccurrences.reduce((a, b) => a.generation < b.generation ? a : b);
+    const closestDam  = damOccurrences.reduce((a, b)  => a.generation < b.generation ? a : b);
+    commonAncestorList.push({
+      id:      ancId,
+      name:    sireOccurrences[0].name,
+      sireGen: closestSire.generation,
+      damGen:  closestDam.generation
     });
   });
-  
-  // Calculate COI using path coefficient method
-  let coi = 0;
-  const processed = new Set();
-  
-  commonAncestors.forEach(anc => {
-    const key = `${anc.id}-${anc.sireGen}-${anc.damGen}`;
-    if (!processed.has(key)) {
-      processed.add(key);
-      const pathLength = anc.sireGen + anc.damGen;
-      coi += Math.pow(0.5, pathLength);
-    }
-  });
-  
+
   return {
-    coefficient: Math.round(coi * 10000) / 100, // Percentage with 2 decimals
-    commonAncestors: [...new Map(commonAncestors.map(a => [a.id, a])).values()]
+    coefficient:     Math.round(coi * 10000) / 100,
+    commonAncestors: commonAncestorList
   };
 }
 
@@ -73,38 +106,34 @@ router.get('/:id', (req, res) => {
   try {
     const db = getDatabase();
     const generations = parseInt(req.query.generations) || 5;
-    
+
     function buildTree(dogId, currentGen = 0) {
       if (currentGen >= generations) return null;
-      
+
       const dog = db.prepare('SELECT * FROM dogs WHERE id = ?').get(dogId);
       if (!dog) return null;
-      
+
       dog.photo_urls = dog.photo_urls ? JSON.parse(dog.photo_urls) : [];
-      
+
       const parents = db.prepare(`
         SELECT p.parent_type, p.parent_id
         FROM parents p
         WHERE p.dog_id = ?
       `).all(dogId);
-      
+
       const sire = parents.find(p => p.parent_type === 'sire');
-      const dam = parents.find(p => p.parent_type === 'dam');
-      
+      const dam  = parents.find(p => p.parent_type === 'dam');
+
       return {
         ...dog,
         generation: currentGen,
         sire: sire ? buildTree(sire.parent_id, currentGen + 1) : null,
-        dam: dam ? buildTree(dam.parent_id, currentGen + 1) : null
+        dam:  dam  ? buildTree(dam.parent_id,  currentGen + 1) : null
       };
     }
-    
+
     const tree = buildTree(req.params.id);
-    
-    if (!tree) {
-      return res.status(404).json({ error: 'Dog not found' });
-    }
-    
+    if (!tree) return res.status(404).json({ error: 'Dog not found' });
     res.json(tree);
   } catch (error) {
     res.status(500).json({ error: error.message });
@@ -116,35 +145,31 @@ router.get('/:id/descendants', (req, res) => {
   try {
     const db = getDatabase();
     const generations = parseInt(req.query.generations) || 3;
-    
+
     function buildDescendantTree(dogId, currentGen = 0) {
       if (currentGen >= generations) return null;
-      
+
       const dog = db.prepare('SELECT * FROM dogs WHERE id = ?').get(dogId);
       if (!dog) return null;
-      
+
       dog.photo_urls = dog.photo_urls ? JSON.parse(dog.photo_urls) : [];
-      
+
       const offspring = db.prepare(`
         SELECT DISTINCT d.id, d.name, d.sex, d.birth_date
         FROM dogs d
         JOIN parents p ON d.id = p.dog_id
         WHERE p.parent_id = ? AND d.is_active = 1
       `).all(dogId);
-      
+
       return {
         ...dog,
         generation: currentGen,
         offspring: offspring.map(child => buildDescendantTree(child.id, currentGen + 1))
       };
     }
-    
+
     const tree = buildDescendantTree(req.params.id);
-    
-    if (!tree) {
-      return res.status(404).json({ error: 'Dog not found' });
-    }
-    
+    if (!tree) return res.status(404).json({ error: 'Dog not found' });
     res.json(tree);
   } catch (error) {
     res.status(500).json({ error: error.message });
@@ -155,28 +180,29 @@ router.get('/:id/descendants', (req, res) => {
 router.post('/trial-pairing', (req, res) => {
   try {
     const { sire_id, dam_id } = req.body;
-    
+
     if (!sire_id || !dam_id) {
       return res.status(400).json({ error: 'Both sire_id and dam_id are required' });
     }
-    
+
     const db = getDatabase();
-    // FIX: use single quotes for string literals — SQLite treats double quotes as identifiers
     const sire = db.prepare("SELECT * FROM dogs WHERE id = ? AND sex = 'male'").get(sire_id);
     const dam  = db.prepare("SELECT * FROM dogs WHERE id = ? AND sex = 'female'").get(dam_id);
-    
+
     if (!sire || !dam) {
       return res.status(404).json({ error: 'Invalid sire or dam' });
     }
-    
+
     const result = calculateCOI(sire_id, dam_id);
-    
+
     res.json({
-      sire: { id: sire.id, name: sire.name },
-      dam: { id: dam.id, name: dam.name },
-      coi: result.coefficient,
+      sire:           { id: sire.id, name: sire.name },
+      dam:            { id: dam.id,  name: dam.name  },
+      coi:            result.coefficient,
       commonAncestors: result.commonAncestors,
-      recommendation: result.coefficient < 5 ? 'Low risk' : result.coefficient < 10 ? 'Moderate risk' : 'High risk'
+      recommendation: result.coefficient < 5  ? 'Low risk'
+                    : result.coefficient < 10 ? 'Moderate risk'
+                    :                           'High risk'
     });
   } catch (error) {
     res.status(500).json({ error: error.message });