diff --git a/package-lock.json b/package-lock.json
index d95e5d8..069c3c7 100644
--- a/package-lock.json
+++ b/package-lock.json
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       "resolved": "https://registry.npmjs.org/zod/-/zod-4.3.6.tgz",
       "integrity": "sha512-rftlrkhHZOcjDwkGlnUtZZkvaPHCsDATp4pGpuOOMDaTdDDXF91wuVDJoWoPsKX/3YPQ5fHuF3STjcYyKr+Qhg==",
       "license": "MIT",
+      "peer": true,
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
       }
diff --git a/package.json b/package.json
index 66bf7ce..f4ecfa4 100644
--- a/package.json
+++ b/package.json
@@ -23,6 +23,7 @@
     "@radix-ui/react-icons": "^1.3.2",
     "@stellar/stellar-sdk": "^11.2.2",
     "clsx": "^2.1.1",
+    "fast-check": "^4.8.0",
     "i18next": "^25.10.9",
     "iron-session": "^8.0.4",
     "lru-cache": "^11.2.6",
diff --git a/tests/property/validation-properties.test.ts b/tests/property/validation-properties.test.ts
index 6179be0..2887dd9 100644
--- a/tests/property/validation-properties.test.ts
+++ b/tests/property/validation-properties.test.ts
@@ -1,4 +1,4 @@
-import { describe, it } from 'vitest';
+import { describe, it, expect } from 'vitest';
 import * as fc from 'fast-check';
 import {
   validateAmount,
@@ -6,6 +6,12 @@ import {
   validateGoalId,
   validateGoalName,
 } from '@/lib/validation/savings-goals';
+import {
+  validatePercentages,
+  validateStellarAddress,
+  ValidationError,
+  SplitPercentages,
+} from '@/lib/validation/percentages';
 
 /**
  * Property-Based Tests for Validation Functions
@@ -151,9 +157,10 @@ describe('Validation Properties - Property-Based Tests', () => {
    * the date validation should return isValid: false.
    */
   it('Property 5: Future date validation rejects past dates', () => {
+    const now = Date.now();
     fc.assert(
       fc.property(
-        fc.date({ max: new Date(Date.now() - 1000) }), // At least 1 second in the past
+        fc.date({ max: new Date(now - 1000) }).filter(d => !isNaN(d.getTime())), // At least 1 second in the past
         (pastDate) => {
           const result = validateFutureDate(pastDate.toISOString());
           return result.isValid === false && result.error?.includes('future');
@@ -164,9 +171,10 @@ describe('Validation Properties - Property-Based Tests', () => {
   });
 
   it('Property 5 (positive case): Future date validation accepts future dates', () => {
+    const now = Date.now();
     fc.assert(
       fc.property(
-        fc.date({ min: new Date(Date.now() + 60000) }), // At least 1 minute in the future
+        fc.date({ min: new Date(now + 60000) }).filter(d => !isNaN(d.getTime())), // At least 1 minute in the future
         (futureDate) => {
           const result = validateFutureDate(futureDate.toISOString());
           return result.isValid === true;
@@ -176,6 +184,122 @@ describe('Validation Properties - Property-Based Tests', () => {
     );
   });
 
+  /**
+   * Property 10: Percentage validation accepts sets that sum to ~100
+   */
+  it('Property 10: validatePercentages accepts sets that sum to 100', () => {
+    fc.assert(
+      fc.property(
+        fc.array(fc.double({ min: 0, max: 100, noNaN: true, noDefaultInfinity: true }), { minLength: 4, maxLength: 4 }),
+        (arr) => {
+          const total = arr.reduce((s, v) => s + v, 0);
+          const factor = total === 0 ? 0 : 100 / total;
+          const percentages: SplitPercentages = {
+            spending: total === 0 ? 25 : arr[0] * factor,
+            savings: total === 0 ? 25 : arr[1] * factor,
+            bills: total === 0 ? 25 : arr[2] * factor,
+            insurance: total === 0 ? 25 : arr[3] * factor,
+          };
+          
+          // Should not throw
+          expect(() => validatePercentages(percentages)).not.toThrow();
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  it('Property 11: validatePercentages rejects negative values', () => {
+    fc.assert(
+      fc.property(
+        fc.integer({ min: 0, max: 3 }),
+        fc.double({ min: -100, max: -0.01, noNaN: true, noDefaultInfinity: true }),
+        (negativeIndex, negativeValue) => {
+          const p: SplitPercentages = { spending: 25, savings: 25, bills: 25, insurance: 25 };
+          const keys = ['spending', 'savings', 'bills', 'insurance'] as const;
+          p[keys[negativeIndex]] = negativeValue;
+          
+          expect(() => validatePercentages(p)).toThrow('must be non-negative');
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  it('Property 12: validatePercentages rejects sums not equal to 100', () => {
+    fc.assert(
+      fc.property(
+        fc.double({ noNaN: true, noDefaultInfinity: true }).filter(s => Math.abs(s - 100) > 0.1),
+        (invalidSum) => {
+          const p: SplitPercentages = { 
+            spending: invalidSum / 4, 
+            savings: invalidSum / 4, 
+            bills: invalidSum / 4, 
+            insurance: invalidSum / 4 
+          };
+          // Filter out negative results which might trigger the negative value check first
+          if (p.spending < 0) return true; 
+
+          try {
+            validatePercentages(p);
+            return false;
+          } catch (e) {
+            return (e as Error).message.includes('sum');
+          }
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  /**
+   * Property 13: validateStellarAddress accepts valid-looking addresses
+   * 
+   * NOTE: This validator uses a regex check (^G[A-Z0-9]{55}$) which is a 
+   * structural check only. It does NOT verify the Base32 checksum or use 
+   * the Stellar StrKey encoding validation (which uses CRC16).
+   * 
+   * Discrepancy: The UI (RecipientAddressInput) uses a stricter validation 
+   * that includes checksum verification. The server-side regex is a 
+   * permissive fallback. The intended source of truth for full validation 
+   * should be the Stellar SDK's StrKey.decodeEd25519PublicKey, but for 
+   * basic property coverage, we verify the regex's invariants.
+   */
+  it('Property 13: validateStellarAddress accepts valid-looking addresses', () => {
+    const stellarAlphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'.split('');
+    fc.assert(
+      fc.property(
+        fc.array(fc.constantFrom(...stellarAlphabet), { minLength: 55, maxLength: 55 }),
+        (arr) => {
+          const address = 'G' + arr.join('');
+          expect(() => validateStellarAddress(address)).not.toThrow();
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
+  it('Property 14: validateStellarAddress rejects adversarial inputs', () => {
+    fc.assert(
+      fc.property(
+        fc.oneof(
+          fc.string().filter(s => s.length !== 56), // Wrong length
+          fc.string({ minLength: 56, maxLength: 56 }).filter(s => !s.startsWith('G')), // Wrong prefix
+          fc.string({ minLength: 56, maxLength: 56, alphabet: 'abcdefghijklmnopqrstuvwxyz' }), // Lowercase
+          fc.string({ minLength: 56, maxLength: 56 }).filter(s => /[^A-Z0-9]/.test(s)), // Illegal characters
+          fc.constant(''), // Empty
+          fc.constant(null as any), // Non-string
+          fc.constant(undefined as any) // Non-string
+        ),
+        (invalidAddress) => {
+          // All these should throw ValidationError
+          expect(() => validateStellarAddress(invalidAddress)).toThrow();
+        }
+      ),
+      { numRuns: 100 }
+    );
+  });
+
   /**
    * Property 9: Error responses have consistent structure
    * Validates: Requirements 8.2
@@ -205,3 +329,4 @@ describe('Validation Properties - Property-Based Tests', () => {
     );
   });
 });
+