Why does 0.1 + 0.2 equal 0.30000000000000004 on most calculators?

Because 0.1 and 0.2 cannot be written exactly in binary floating point — they are stored as the nearest binary approximations, and the tiny errors show up in the sum. BigInt avoids this entirely by storing integers digit by digit instead of as binary fractions.

How large can the numbers be here?

There is no fixed digit limit — BigInt uses arbitrary precision, bounded only by your device’s memory. Hundreds or thousands of digits compute instantly; the result’s digit count is shown so you can verify the scale.

Why can’t I enter decimals like 3.5?

Exactness is only well-defined for whole numbers in this calculator. BigInt is an integer type, so decimal inputs are rejected rather than silently approximated — enter the integer part, or scale your values (for example, work in cents instead of dollars).

How many digits are in 100000000000000000001?

Twenty-one. It is 10²⁰ + 1, and this calculator returns all 21 digits exactly — compare that with a floating-point calculator, which rounds the answer back to 100000000000000000000.

Big Number Calculator

Add, subtract, multiply, divide, and find GCDs of huge integers with exact BigInt arithmetic — no float rounding, ever. Handles numbers with hundreds of digits, shows digit counts, and compares the exact answer against what ordinary floating-point math would give. Results update instantly. Free, no sign-up.

First integer

Second integer

Operation

Advanced options

Group digits in thousands (1,000,000)

Also show powers: A² and 2^digits

Why Ordinary Calculators Get Big Numbers Wrong

Standard computer numbers (64-bit floats) can only represent integers exactly up to 9,007,199,254,740,991. Beyond that they start rounding: 123456789 × 987654321 comes out as 121932631112635260 instead of …269. The last digits silently go wrong — dangerous for cryptography, finance, and combinatorics.

BigInt arithmetic uses as much memory as the number needs, so every digit is exact no matter how large. The comparison below runs your calculation both ways so you can see exactly where floating point starts lying.

Where Exact Big Integers Matter

RSA encryption multiplies primes with 600+ digits; national debts and astronomical distances need exact large integers; factorials explode fast (100! has 158 digits). Whenever rounding is not an option, exact integer math is the tool.

Frequently Asked Questions

What is 123456789 × 987654321 exactly?

121,932,631,112,635,269 — all 18 digits exact. A normal calculator gives …260, off by 9.

What is the largest exact integer in JavaScript?

9,007,199,254,740,991 (2^53 − 1) for regular numbers. BigInt has no such limit.

Can BigInt do decimals or division?

BigInt is integers only — division truncates toward zero. The ÷ and % modes show quotient + remainder, and GCD uses the Euclidean algorithm — exact at any size.

How many digits can this handle?

Hundreds of digits comfortably. Try 100-digit numbers — the answer stays digit-perfect.

Why do floats round large integers?

A 64-bit float has 53 bits of precision (~15–16 decimal digits). Bigger integers must be rounded to fit.

Big Number Calculator

Why Ordinary Calculators Get Big Numbers Wrong

Where Exact Big Integers Matter

Frequently Asked Questions

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