diff --git a/common/src/util/__tests__/currency.test.ts b/common/src/util/__tests__/currency.test.ts
new file mode 100644
index 0000000000..757d6b4003
--- /dev/null
+++ b/common/src/util/__tests__/currency.test.ts
@@ -0,0 +1,56 @@
+import { describe, expect, it } from 'bun:test'
+
+import {
+  convertCreditsToUsdCents,
+  convertStripeGrantAmountToCredits,
+} from '../currency'
+
+describe('convertCreditsToUsdCents', () => {
+  it('converts credits to cents correctly', () => {
+    expect(convertCreditsToUsdCents(1, 100)).toBe(100)
+    expect(convertCreditsToUsdCents(1.5, 100)).toBe(150)
+    expect(convertCreditsToUsdCents(0.1, 100)).toBe(10)
+  })
+
+  it('throws for non-positive centsPerCredit', () => {
+    expect(() => convertCreditsToUsdCents(100, 0)).toThrow('centsPerCredit must be positive')
+    expect(() => convertCreditsToUsdCents(100, -10)).toThrow('centsPerCredit must be positive')
+  })
+
+  it('throws for NaN credits', () => {
+    expect(() => convertCreditsToUsdCents(NaN, 100)).toThrow('credits must be finite')
+  })
+
+  it('throws for Infinity credits', () => {
+    expect(() => convertCreditsToUsdCents(Infinity, 100)).toThrow('credits must be finite')
+  })
+
+  it('throws for negative Infinity credits', () => {
+    expect(() => convertCreditsToUsdCents(-Infinity, 100)).toThrow('credits must be finite')
+  })
+})
+
+describe('convertStripeGrantAmountToCredits', () => {
+  it('converts cents to credits correctly', () => {
+    expect(convertStripeGrantAmountToCredits(10000, 100)).toBe(100)
+    expect(convertStripeGrantAmountToCredits(15000, 100)).toBe(150)
+    expect(convertStripeGrantAmountToCredits(1000, 100)).toBe(10)
+  })
+
+  it('throws for non-positive centsPerCredit', () => {
+    expect(() => convertStripeGrantAmountToCredits(10000, 0)).toThrow('centsPerCredit must be positive')
+    expect(() => convertStripeGrantAmountToCredits(10000, -10)).toThrow('centsPerCredit must be positive')
+  })
+
+  it('throws for NaN amountInCents', () => {
+    expect(() => convertStripeGrantAmountToCredits(NaN, 100)).toThrow('amountInCents must be finite')
+  })
+
+  it('throws for Infinity amountInCents', () => {
+    expect(() => convertStripeGrantAmountToCredits(Infinity, 100)).toThrow('amountInCents must be finite')
+  })
+
+  it('throws for negative Infinity amountInCents', () => {
+    expect(() => convertStripeGrantAmountToCredits(-Infinity, 100)).toThrow('amountInCents must be finite')
+  })
+})
\ No newline at end of file
diff --git a/common/src/util/currency.ts b/common/src/util/currency.ts
index b3499c01e5..ccdbc5cca6 100644
--- a/common/src/util/currency.ts
+++ b/common/src/util/currency.ts
@@ -3,11 +3,22 @@
  * @param credits The number of credits to convert
  * @param centsPerCredit The cost per credit in cents
  * @returns The amount in USD cents
+ * @throws Error if centsPerCredit is not positive or credits is not finite
  */
 export function convertCreditsToUsdCents(
   credits: number,
   centsPerCredit: number,
 ): number {
+  if (!(centsPerCredit > 0)) {
+    throw new Error(
+      `convertCreditsToUsdCents: centsPerCredit must be positive, got ${centsPerCredit}`,
+    )
+  }
+  if (!Number.isFinite(credits)) {
+    throw new Error(
+      `convertCreditsToUsdCents: credits must be finite, got ${credits}`,
+    )
+  }
   return Math.ceil(credits * centsPerCredit)
 }
 
@@ -16,10 +27,21 @@ export function convertCreditsToUsdCents(
  * @param amountInCents The amount in USD cents
  * @param centsPerCredit The cost per credit in cents
  * @returns The number of credits
+ * @throws Error if centsPerCredit is not positive or amountInCents is not finite
  */
 export function convertStripeGrantAmountToCredits(
   amountInCents: number,
   centsPerCredit: number,
 ): number {
+  if (!(centsPerCredit > 0)) {
+    throw new Error(
+      `convertStripeGrantAmountToCredits: centsPerCredit must be positive, got ${centsPerCredit}`,
+    )
+  }
+  if (!Number.isFinite(amountInCents)) {
+    throw new Error(
+      `convertStripeGrantAmountToCredits: amountInCents must be finite, got ${amountInCents}`,
+    )
+  }
   return Math.floor(amountInCents / centsPerCredit)
 }