diff --git a/js/payments/platformFee.js b/js/payments/platformFee.js
new file mode 100644
index 00000000..c448b15a
--- /dev/null
+++ b/js/payments/platformFee.js
@@ -0,0 +1,74 @@
+// js/payments/platformFee.js
+
+import { PLATFORM_FEE_PERCENT } from "../config.js";
+
+export function parsePercentValue(value) {
+  if (typeof value === "number") {
+    return Number.isFinite(value) ? value : NaN;
+  }
+
+  if (typeof value === "bigint") {
+    return Number(value);
+  }
+
+  if (typeof value === "string") {
+    const trimmed = value.trim();
+    if (!trimmed) {
+      return NaN;
+    }
+
+    if (trimmed.includes("/")) {
+      const [firstRaw, secondRaw] = trimmed.split("/").map((part) => part.trim());
+      if (firstRaw && secondRaw) {
+        const first = Number(firstRaw);
+        const second = Number(secondRaw);
+        if (Number.isFinite(first) && Number.isFinite(second) && first >= 0 && second >= 0) {
+          const total = first + second;
+          if (total > 0) {
+            return (second / total) * 100;
+          }
+        }
+      }
+    }
+
+    const percentStripped = trimmed.endsWith("%") ? trimmed.slice(0, -1).trim() : trimmed;
+    const directNumeric = Number(percentStripped);
+    if (Number.isFinite(directNumeric)) {
+      return directNumeric;
+    }
+
+    const match = percentStripped.match(/-?\d+(?:\.\d+)?/);
+    if (match) {
+      const fallback = Number(match[0]);
+      return Number.isFinite(fallback) ? fallback : NaN;
+    }
+
+    return NaN;
+  }
+
+  return Number.isFinite(value) ? Number(value) : NaN;
+}
+
+export function clampPercent(value) {
+  const numeric = parsePercentValue(value);
+  if (!Number.isFinite(numeric)) {
+    return 0;
+  }
+  return Math.min(100, Math.max(0, numeric));
+}
+
+export function getDefaultPlatformFeePercent() {
+  const parsed = parsePercentValue(PLATFORM_FEE_PERCENT);
+  if (!Number.isFinite(parsed)) {
+    return 0;
+  }
+  return clampPercent(parsed);
+}
+
+export function resolvePlatformFeePercent(overrideValue) {
+  const parsedOverride = parsePercentValue(overrideValue);
+  if (Number.isFinite(parsedOverride)) {
+    return clampPercent(parsedOverride);
+  }
+  return getDefaultPlatformFeePercent();
+}
diff --git a/js/payments/zapSharedState.js b/js/payments/zapSharedState.js
index 5aaccc04..21cc7746 100644
--- a/js/payments/zapSharedState.js
+++ b/js/payments/zapSharedState.js
@@ -1,4 +1,4 @@
-import { PLATFORM_FEE_PERCENT } from "../config.js";
+import { resolvePlatformFeePercent } from "./platformFee.js";
 import {
   resolveLightningAddress as defaultResolveLightningAddress,
   fetchPayServiceData as defaultFetchPayServiceData,
@@ -112,11 +112,9 @@ export async function fetchLightningMetadata(
 
 export function calculateZapShares(amount, overrideFee = null) {
   const numericAmount = Math.max(0, Math.round(Number(amount) || 0));
-  const percentSource =
-    typeof overrideFee === "number" && Number.isFinite(overrideFee)
-      ? overrideFee
-      : PLATFORM_FEE_PERCENT;
-  const feePercent = Math.min(100, Math.max(0, Math.round(percentSource)));
+  const feePercent = resolvePlatformFeePercent(
+    typeof overrideFee === "undefined" ? null : overrideFee
+  );
   const platformShare = Math.floor((numericAmount * feePercent) / 100);
   const creatorShare = numericAmount - platformShare;
   return {
diff --git a/js/payments/zapSplit.js b/js/payments/zapSplit.js
index a42ba18d..06bb25ff 100644
--- a/js/payments/zapSplit.js
+++ b/js/payments/zapSplit.js
@@ -1,6 +1,6 @@
 // js/payments/zapSplit.js
 
-import { PLATFORM_FEE_PERCENT, ADMIN_SUPER_NPUB } from "../config.js";
+import { ADMIN_SUPER_NPUB } from "../config.js";
 import {
   resolveLightningAddress,
   fetchPayServiceData,
@@ -9,6 +9,11 @@ import {
 } from "./lnurl.js";
 import { ensureWallet, sendPayment } from "./nwcClient.js";
 import { getPlatformLightningAddress } from "./platformAddress.js";
+import {
+  clampPercent,
+  parsePercentValue,
+  resolvePlatformFeePercent,
+} from "./platformFee.js";
 
 const HEX64_REGEX = /^[0-9a-f]{64}$/i;
 const ZAP_KIND = 9734;
@@ -24,19 +29,7 @@ const DEFAULT_DEPS = Object.freeze({
 });
 
 function getOverridePlatformFee() {
-  const override = globalThis?.__BITVID_PLATFORM_FEE_OVERRIDE__;
-  if (Number.isFinite(override)) {
-    return override;
-  }
-  return PLATFORM_FEE_PERCENT;
-}
-
-function clampPercent(value) {
-  const numeric = Number(value);
-  if (!Number.isFinite(numeric)) {
-    return 0;
-  }
-  return Math.min(100, Math.max(0, numeric));
+  return resolvePlatformFeePercent(globalThis?.__BITVID_PLATFORM_FEE_OVERRIDE__);
 }
 
 function sanitizeAmount(amount) {
@@ -341,4 +334,6 @@ export const __TESTING__ = Object.freeze({
   determineRecipientPubkey,
   derivePointerTag,
   mergeDependencies,
+  parsePercentValue,
+  clampPercent,
 });
diff --git a/tests/zap-shared-state.test.mjs b/tests/zap-shared-state.test.mjs
new file mode 100644
index 00000000..f3f11e98
--- /dev/null
+++ b/tests/zap-shared-state.test.mjs
@@ -0,0 +1,29 @@
+import assert from "node:assert/strict";
+
+const sharedStateModule = await import("../js/payments/zapSharedState.js");
+const feeModule = await import("../js/payments/platformFee.js");
+
+const { calculateZapShares } = sharedStateModule;
+const { resolvePlatformFeePercent } = feeModule;
+
+(function testCalculateZapSharesSupportsRatioOverride() {
+  const result = calculateZapShares(35, "70/30");
+  assert.equal(result.total, 35);
+  assert.equal(result.platformShare, 10);
+  assert.equal(result.creatorShare, 25);
+  assert.equal(result.feePercent, 30);
+})();
+
+(function testCalculateZapSharesHandlesPercentStrings() {
+  const result = calculateZapShares(200, "30% ");
+  assert.equal(result.platformShare, 60);
+  assert.equal(result.creatorShare, 140);
+  assert.equal(result.feePercent, 30);
+})();
+
+(function testResolvePlatformFeePercentFallsBackToDefault() {
+  const percent = resolvePlatformFeePercent("not-a-number");
+  assert.equal(percent, 0);
+})();
+
+console.log("zap-shared-state tests passed");
diff --git a/tests/zap-split.test.mjs b/tests/zap-split.test.mjs
index 22962299..b683ce2c 100644
--- a/tests/zap-split.test.mjs
+++ b/tests/zap-split.test.mjs
@@ -180,6 +180,42 @@ async function testSplitMath() {
   delete globalThis.__BITVID_PLATFORM_FEE_OVERRIDE__;
 }
 
+async function testStringFeeOverride() {
+  const videoEvent = {
+    id: "event-id",
+    pubkey: "c".repeat(64),
+    lightningAddress: "creator@example.com",
+    tags: [["d", "pointer"]],
+    kind: 30078,
+  };
+
+  globalThis.__BITVID_PLATFORM_FEE_OVERRIDE__ = "70/30";
+  const seventyThirty = createDeps();
+  const ratioResult = await splitAndZap(
+    { videoEvent, amountSats: 1000, comment: "Great video!" },
+    seventyThirty.deps
+  );
+
+  assert.equal(ratioResult.creatorShare, 700);
+  assert.equal(ratioResult.platformShare, 300);
+  const ratioSendCalls = seventyThirty.getSendCalls();
+  assert.equal(ratioSendCalls.length, 2, "should send two payments for ratio");
+  assert.equal(ratioSendCalls[0].amountSats, 700);
+  assert.equal(ratioSendCalls[1].amountSats, 300);
+
+  globalThis.__BITVID_PLATFORM_FEE_OVERRIDE__ = "30%";
+  const percentOverride = createDeps();
+  const percentResult = await splitAndZap(
+    { videoEvent, amountSats: 200, comment: "Another zap" },
+    percentOverride.deps
+  );
+
+  assert.equal(percentResult.creatorShare, 140);
+  assert.equal(percentResult.platformShare, 60);
+
+  delete globalThis.__BITVID_PLATFORM_FEE_OVERRIDE__;
+}
+
 async function testLnurlBounds() {
   globalThis.__BITVID_PLATFORM_FEE_OVERRIDE__ = 0;
   const depsWrapper = createDeps({ minSendable: 5_000 });
@@ -265,5 +301,6 @@ await testSplitMath();
 await testLnurlBounds();
 await testMissingAddress();
 await testWalletFailure();
+await testStringFeeOverride();
 
 console.log("zap-split tests passed");