diff --git a/packages/morpho-ts/src/format/format/README.md b/packages/morpho-ts/src/format/format/README.md
index 73faeb69..82a68a83 100644
--- a/packages/morpho-ts/src/format/format/README.md
+++ b/packages/morpho-ts/src/format/format/README.md
@@ -23,7 +23,7 @@ The `format` object provides access to different formatters:
 ### Usage
 
 Each formatter can be accessed through the `format` object and provides chainable methods to customize the output. The formatted value can be obtained calling `.of(value)` for `number` or `.of(value, decimals)` for `bigint`.
-The return value will retain the nullability of the input value, unless a `.default()` method is applied (refer to [Number Formatter](#2-number-formatter) for details).
+The return value will retain the nullability of the input value (giving priority to `value` over `decimals` for bigints, if none is defined), unless a `.default()` method is applied (refer to [Number Formatter](#2-number-formatter) for details).
 
 > [!Tip]
 > You can store the populated `of` function in a custom formatter:
@@ -71,7 +71,7 @@ const numberValue = format.number.of(123.45); // "123.45"
 - `.unit(string)`: Adds a unit to the number (e.g., "$", "%").
 - `.locale(string)`: Formats the number according to the specified locale.
 - `.readable()`: Makes the value more readable for small numbers.
-- `.default(string)`: Sets a default value in case value is `null` or `undefined`.
+- `.default(string)`: Sets a default value in case `value` (or `decimals`) is `null` or `undefined`.
 
 ### 3. Commas Formatter
 
diff --git a/packages/morpho-ts/src/format/format/format.test.ts b/packages/morpho-ts/src/format/format/format.test.ts
index 72982719..744e3562 100644
--- a/packages/morpho-ts/src/format/format/format.test.ts
+++ b/packages/morpho-ts/src/format/format/format.test.ts
@@ -14,6 +14,10 @@ describe("format", () => {
         expect(format.hex.default("default").of(undefined)).toEqual("default");
         expect(format.hex.default("default").of(null)).toEqual("default");
       });
+      it("with nullable values", () => {
+        expect(format.hex.of(undefined)).toEqual(undefined);
+        expect(format.hex.of(null)).toEqual(null);
+      });
     });
     describe("should properly format bigint in hex format", () => {
       it("without option", () => {
@@ -26,6 +30,20 @@ describe("format", () => {
           "default",
         );
         expect(format.hex.default("default").of(null, 18)).toEqual("default");
+        expect(format.hex.default("default").of(bigint, undefined)).toEqual(
+          "default",
+        );
+        expect(format.hex.default("default").of(bigint, null)).toEqual(
+          "default",
+        );
+      });
+      it("with nullable values", () => {
+        expect(format.hex.of(undefined, decimals)).toEqual(undefined);
+        expect(format.hex.of(null, decimals)).toEqual(null);
+        expect(format.hex.of(bigint, undefined)).toEqual(undefined);
+        expect(format.hex.of(bigint, null)).toEqual(null);
+        expect(format.hex.of(null, undefined)).toEqual(null);
+        expect(format.hex.of(undefined, null)).toEqual(undefined);
       });
     });
   });
@@ -76,6 +94,10 @@ describe("format", () => {
         );
         expect(format.number.default("default").of(null)).toEqual("default");
       });
+      it("with nullable values", () => {
+        expect(format.number.of(undefined)).toEqual(undefined);
+        expect(format.number.of(null)).toEqual(null);
+      });
     });
     describe("should properly format bigint in number format", () => {
       it("without option", () => {
@@ -126,6 +148,20 @@ describe("format", () => {
         expect(format.number.default("default").of(null, 18)).toEqual(
           "default",
         );
+        expect(format.number.default("default").of(bigint, undefined)).toEqual(
+          "default",
+        );
+        expect(format.number.default("default").of(bigint, null)).toEqual(
+          "default",
+        );
+      });
+      it("with nullable values", () => {
+        expect(format.number.of(undefined, decimals)).toEqual(undefined);
+        expect(format.number.of(null, decimals)).toEqual(null);
+        expect(format.number.of(bigint, undefined)).toEqual(undefined);
+        expect(format.number.of(bigint, null)).toEqual(null);
+        expect(format.number.of(null, undefined)).toEqual(null);
+        expect(format.number.of(undefined, null)).toEqual(undefined);
       });
     });
   });
@@ -170,6 +206,10 @@ describe("format", () => {
         );
         expect(format.short.default("default").of(null)).toEqual("default");
       });
+      it("with nullable values", () => {
+        expect(format.short.of(undefined)).toEqual(undefined);
+        expect(format.short.of(null)).toEqual(null);
+      });
     });
     describe("should properly format bigint in short format", () => {
       it("without option", () => {
@@ -230,6 +270,20 @@ describe("format", () => {
           "default",
         );
         expect(format.short.default("default").of(null, 18)).toEqual("default");
+        expect(format.short.default("default").of(bigint, undefined)).toEqual(
+          "default",
+        );
+        expect(format.short.default("default").of(bigint, null)).toEqual(
+          "default",
+        );
+      });
+      it("with nullable values", () => {
+        expect(format.short.of(undefined, decimals)).toEqual(undefined);
+        expect(format.short.of(null, decimals)).toEqual(null);
+        expect(format.short.of(bigint, undefined)).toEqual(undefined);
+        expect(format.short.of(bigint, null)).toEqual(null);
+        expect(format.short.of(null, undefined)).toEqual(null);
+        expect(format.short.of(undefined, null)).toEqual(undefined);
       });
     });
   });
@@ -271,6 +325,10 @@ describe("format", () => {
         );
         expect(format.commas.default("default").of(null)).toEqual("default");
       });
+      it("with nullable values", () => {
+        expect(format.commas.of(undefined)).toEqual(undefined);
+        expect(format.commas.of(null)).toEqual(null);
+      });
     });
     describe("should properly format bigint in commas format", () => {
       it("without option", () => {
@@ -322,6 +380,20 @@ describe("format", () => {
         expect(format.commas.default("default").of(null, 18)).toEqual(
           "default",
         );
+        expect(format.commas.default("default").of(bigint, undefined)).toEqual(
+          "default",
+        );
+        expect(format.commas.default("default").of(bigint, null)).toEqual(
+          "default",
+        );
+      });
+      it("with nullable values", () => {
+        expect(format.commas.of(undefined, decimals)).toEqual(undefined);
+        expect(format.commas.of(null, decimals)).toEqual(null);
+        expect(format.commas.of(bigint, undefined)).toEqual(undefined);
+        expect(format.commas.of(bigint, null)).toEqual(null);
+        expect(format.commas.of(null, undefined)).toEqual(null);
+        expect(format.commas.of(undefined, null)).toEqual(undefined);
       });
     });
   });
@@ -362,6 +434,10 @@ describe("format", () => {
         );
         expect(format.percent.default("default").of(null)).toEqual("default");
       });
+      it("with nullable values", () => {
+        expect(format.percent.of(undefined)).toEqual(undefined);
+        expect(format.percent.of(null)).toEqual(null);
+      });
     });
     describe("should properly format bigint in percent format", () => {
       it("without option", () => {
@@ -409,6 +485,20 @@ describe("format", () => {
         expect(format.percent.default("default").of(null, 18)).toEqual(
           "default",
         );
+        expect(format.percent.default("default").of(bigint, undefined)).toEqual(
+          "default",
+        );
+        expect(format.percent.default("default").of(bigint, null)).toEqual(
+          "default",
+        );
+      });
+      it("with nullable values", () => {
+        expect(format.percent.of(undefined, decimals)).toEqual(undefined);
+        expect(format.percent.of(null, decimals)).toEqual(null);
+        expect(format.percent.of(bigint, undefined)).toEqual(undefined);
+        expect(format.percent.of(bigint, null)).toEqual(null);
+        expect(format.percent.of(null, undefined)).toEqual(null);
+        expect(format.percent.of(undefined, null)).toEqual(undefined);
       });
     });
   });
diff --git a/packages/morpho-ts/src/format/format/format.ts b/packages/morpho-ts/src/format/format/format.ts
index e09e15be..4d101099 100644
--- a/packages/morpho-ts/src/format/format/format.ts
+++ b/packages/morpho-ts/src/format/format/format.ts
@@ -265,7 +265,10 @@ function formatBI(
 }
 
 type FormatterWithDefault<F extends BaseFormatter> = {
-  of(value: bigint | null | undefined, decimals: number): string;
+  of(
+    value: bigint | null | undefined,
+    decimals: number | null | undefined,
+  ): string;
   of(value: number | null | undefined): string;
 } & {
   [K in keyof Omit<F, "of">]: F[K] extends (...args: infer A) => F
@@ -284,15 +287,19 @@ export abstract class BaseFormatter {
     return this as FormatterWithDefault<this>;
   }
 
-  of<T extends bigint | null | undefined>(
+  of<T extends bigint | null | undefined, D extends number | null | undefined>(
     value: T,
-    decimals: number,
-  ): Exclude<T, bigint> | string;
+    decimals: D,
+  ): Exclude<T, bigint> | Exclude<D, number> | string;
   of<T extends number | null | undefined>(
     value: T,
   ): Exclude<T, number> | string;
-  of(value: bigint | number, decimals?: number) {
-    if (value == null) return this._options.default ?? value;
+  of(
+    value: bigint | number | null | undefined,
+    decimals?: number | null | undefined,
+  ) {
+    if (value == null || (typeof value === "bigint" && decimals == null))
+      return this._options.default ?? (value == null ? value : decimals);
 
     if (typeof value === "number") {
       const str = value.toString();