JavaScript Number MAX_SAFE_INTEGER Property

What You’ll Learn

Number.MAX_SAFE_INTEGER is a static data property on Number (same API as MDN Number.MAX_SAFE_INTEGER). It is the largest integer a JavaScript Number can represent exactly — 253 − 1 (9007199254740991). Beyond it, use BigInt. This tutorial covers its value, the famous +1 === +2 trap, how it relates to EPSILON and MAX_VALUE, five examples, and try-it labs.

Introduction

JavaScript Numbers are IEEE-754 doubles. They can be enormous ((MAX_VALUE), but they cannot label every integer exactly once the magnitude grows. The 52-bit fraction (plus an implicit leading 1) gives 53 bits of integer precision.

Number.MAX_SAFE_INTEGER is 253 − 1 — the top of the range where consecutive integers are still distinct and comparable. Past that point, some integers are skipped.

This page is part of JavaScript Number Properties. Related tools include Number.isSafeInteger(), Number.EPSILON, and Number.MAX_VALUE.

Understanding the MAX_SAFE_INTEGER Property

“Safe” means two things: the integer can be stored exactly, and integer comparisons / increments behave as you expect. Outside −MAX_SAFE_INTEGER … MAX_SAFE_INTEGER, that guarantee breaks.

• It is a constant number, not a method.
• Value: 9007199254740991 (253 − 1).
• Pair with Number.MIN_SAFE_INTEGER for the negative bound (same magnitude).
• For larger exact integers, prefer BigInt.

📝 Syntax

General form of the static property Number.MAX_SAFE_INTEGER:

Number.MAX_SAFE_INTEGER

Value

9007199254740991 (253 − 1).

Property attributes

Common patterns

Number.MAX_SAFE_INTEGER;                 // 9007199254740991
Number.MAX_SAFE_INTEGER === 2 ** 53 - 1; // true

Number.isSafeInteger(Number.MAX_SAFE_INTEGER);     // true
Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1); // false

// Prefer BigInt past the safe range:
9007199254740993n;  // exact

Examples Gallery

Examples follow MDN Number.MAX_SAFE_INTEGER patterns. Use View Output or Try It Yourself for each case.

Number.MAX_SAFE_INTEGER;
// 9007199254740991

9007199254740991

const x = Number.MAX_SAFE_INTEGER + 1;
const y = Number.MAX_SAFE_INTEGER + 2;

Number.MAX_SAFE_INTEGER;  // 9007199254740991
x;                        // 9007199254740992
x === y;                  // true  (!)

9007199254740991
9007199254740992
true

Number.isSafeInteger(Number.MAX_SAFE_INTEGER);     // true
Number.isSafeInteger(Number.MAX_SAFE_INTEGER + 1); // false

true
false

Number.MAX_SAFE_INTEGER * Number.EPSILON;
// 1.9999999999999998  (very close to 2)

1.9999999999999998

Number.MAX_VALUE > Number.MAX_SAFE_INTEGER;  // true
Number.isSafeInteger(Number.MAX_VALUE);      // false

true
false

🚀 Common Use Cases

• ID / counter bounds — keep database keys and counters inside the safe range.
• JSON numbers — JSON has no BigInt; stay ≤ MAX_SAFE_INTEGER or use strings.
• Validation — Number.isSafeInteger(n) before trusting integer math.
• Teaching floats — show why large integers need BigInt.
• Not a magnitude ceiling — use MAX_VALUE for overflow-to-Infinity.
• Timestamps / snowflakes — many 64-bit IDs exceed the safe Number range.

📝 Notes

• This is a static property — use Number.MAX_SAFE_INTEGER only.
• Do not write Number.MAX_SAFE_INTEGER() — it is not a function.
• “Safe” = exact + correctly comparable integers.
• Do not confuse with MAX_VALUE.
• Negative twin: Number.MIN_SAFE_INTEGER (-(253 − 1)).
• For larger exact integers, use BigInt.

💡 Best Practices