Big integer addition calculator
9223372036854775807 plus 1 is exactly 9223372036854775808, a sum that overflows a signed 64-bit integer but is kept here digit by digit. Add two whole numbers of any length, with no rounding or wrap-around, and see whether the result still fits in 64 bits. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- First text
- 9223372036854775807
- Second text
- 1
- Sum
- 9223372036854775808
- Digit count
- 19
- Sign
- positive
Native sixty-four-bit integers stop being exact the moment a sum crosses their representable range. JavaScript numbers lose integer identity past nine quadrillion, signed long values wrap or throw at nine quintillion, and unsigned registers cannot hold two to the sixty-fourth power. This big integer addition calculator accepts two decimal integers of any length, adds them with schoolbook carry arithmetic, and returns the exact decimal sum as a string — no rounding, no wrap-around, and no scientific notation. Add a signed sixty-four-bit maximum to one and you receive 9223372036854775808; add two hundred-digit ledger totals and every digit is kept. Failed validation is not billed.
Why native addition fails and how schoolbook carry stays exact
Every common native integer type has a hard ceiling. A signed sixty-four-bit word tops out at 9223372036854775807; adding one either wraps to a large negative, saturates, or raises overflow. A big integer addition calculator exists to refuse that bargain.
Each operand is read as a signed decimal digit string, leading zeros are stripped, and the two magnitudes are added from the least significant digit with a carry of zero or one, exactly as on paper. When the signs differ the smaller magnitude is subtracted from the larger and the sign of the larger is kept; equal opposite magnitudes cancel to zero. The result is written back as a canonical decimal string with at most one leading minus and no plus sign.
Because every step is a finite digit operation, the sum is exact for any length up to the published digit limit. That is the whole algorithm: no floating point, no modular reduction, no rounding mode. The capability also reports how many digits the absolute value of the sum occupies, whether the sum is positive, negative, or zero, and whether it sits outside the signed sixty-four-bit range, so callers who still have to talk to a fixed-width system know when they must keep the string form.
Where exact big-integer addition earns its keep
Finance and billing pipelines add invoice lines, tax bases, and cryptocurrency subunit totals that already exceed what a spreadsheet cell or a sixty-four-bit money column can hold without rounding. Cryptography and encoding tools add large public integers, serial numbers, and hash-sized counters when they only need a sum, not a full multiprecision library. Computer-science courses and coding-interview practice need an oracle that demonstrates carry propagation on a string of nines plus one, and that refuses to pretend 2^63 minus one plus one still fits in a signed long.
You then have a reproducible exact total for ledgers, graders, and edge workers without standing up an arbitrary-precision arithmetic service of your own.
What you can do with it
Ledger and invoice totals beyond sixty-four bits
Add two money, tax, or subunit amounts that already overflow a signed long or a spreadsheet cell, and keep the exact decimal total as a string.
Overflow oracles for graders and interviews
Check student or candidate adders against a deterministic schoolbook sum, including a string of nines plus one and signed sixty-four-bit overflow.
Migration checks before widening integer columns
Compare a database SUM against this exact total to see whether a column still fits in int64 or must become a decimal or numeric type.
FAQ
How do I add two integers that overflow a sixty-four-bit type?
Send a and b as decimal digit strings (optional leading sign).
Does the calculator wrap or saturate on overflow?
No. The sum is unlimited within the published digit limit. There is no wrap and no clamp. For fixed-width saturating add, use a dedicated saturating-integer tool instead.
Can I add a negative number to a positive one?
Yes. Write a minus sign in front of the negative value. When the signs differ, the smaller magnitude is subtracted from the larger and the larger one's sign is kept; equal and opposite values give zero.
How long can each number be?
Up to 10,000 digits each, counted after leading zeros are removed. Write plain digits with an optional plus or minus sign: thousands separators, spaces, decimals, hexadecimal prefixes and scientific notation are rejected.
Why does a spreadsheet get very large sums wrong?
Many spreadsheet cells store numbers in floating point, which cannot represent every integer beyond 9,007,199,254,740,991, so 10^16 plus one may already be stored as 10^16. Here the digits stay as text and every one of them is kept.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/dev/bignum-add \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"a":"9223372036854775807","b":"1"}'const res = await fetch("https://api.kit.forhosting.com/dev/bignum-add", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"a": "9223372036854775807",
"b": "1"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/dev/bignum-add",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"a": "9223372036854775807",
"b": "1"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/dev/bignum-add", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"a":"9223372036854775807","b":"1"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"a":"9223372036854775807","b":"1"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/dev/bignum-add", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"a": "9223372036854775807",
"b": "1"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "dev.bignum_add",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_digits | 10000 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Successful API calls use the published $0.002 base price.
Why native addition fails and how schoolbook carry stays exact
IEEE-754 doubles, which JSON numbers and many spreadsheet cells actually are, lose the ability to represent every integer once the magnitude passes 9007199254740991, so 10^16 plus one may already be stored as 10^16.
Input contract, response shape, limits, and errors
Empty strings and omitted fields fail the same way. After the sign is read, leading zeros are stripped; a value of minus zero becomes zero. Each stripped magnitude may contain at most 10000 digits — that limit is declared and enforced so a pasted wall of digits cannot exhaust the isolate. Mixed signs work the same way: minus one hundred followed by twenty zeros, plus one, yields a nineteen-digit negative. Validation failures are not billed. POST a JSON object with two required fields, a and b. Each field is a decimal integer: a digit string with an optional leading plus or minus, or a JSON number that is a safe integer. Fractions, thousands separators, spaces inside the digits, hexadecimal prefixes, and scientific notation are rejected with invalid_input naming the field. On success the body echoes the two addends in canonical form, returns sum as the exact decimal total, digit_count as the number of digits in the absolute value, sign as positive, negative, or zero, exceeds_int64 as true when the sum is not representable as a signed sixty-four-bit integer, and a short formula string restating sum equals a plus b. Example: a equals 9223372036854775807 and b equals 1 yields sum 9223372036854775808, digit_count 19, sign positive, and exceeds_int64 true. Successful API calls use the published $0.002 base price.
Where exact big-integer addition earns its keep
Data-migration scripts compare a database SUM of NUMERIC columns against this endpoint to catch silent overflow in an integer column they are about to widen. Keep each operand within the published digit limit, send values that would overflow JSON as strings rather than numbers, and pin the returned sum in tests.
Technical questions
Why must large values be strings instead of JSON numbers?
JSON numbers are IEEE-754 doubles. Integers larger than 9007199254740991 are not all representable, so a value such as 9223372036854775807 would already be rounded before the adder ran. Digit strings stay exact.
What inputs are rejected?
Missing a or b, empty strings, fractions, thousands separators, non-digit characters, and magnitudes longer than 10000 digits fail with invalid_input and are not billed.
What does the big integer addition calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.