How Long Can MySQL INT vs BIGINT Auto‑Increment IDs Last? Calculations & Migration Guide

MySQL auto‑increment primary keys are typically defined as INT (4 bytes) or BIGINT (8 bytes). Both types cover most applications, but when the maximum value is reached, inserts fail with an error such as

ERROR 167 (22003): Out of range value for column 'id' at row 1

.

INT limits and capacity

Signed INT ranges from -2,147,483,648 to 2,147,483,647; unsigned INT ranges from 0 to 4,294,967,295, roughly 4.3 billion values.

Assuming 100 inserts per second, the usable lifespan of an unsigned INT can be calculated:

# INT maximum value
max_int_value = 4294967295
# Inserts per second
records_per_second = 100
# Seconds per year
records_per_year = 365 * 24 * 60 * 60
result = max_int_value / (records_per_second * records_per_year)
print(result)  # 1.3619251950152207 years

The result shows that an unsigned INT would be exhausted in about 1.36 years at that rate, which is insufficient for long‑running systems.

BIGINT limits and capacity

Signed BIGINT spans -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807; unsigned BIGINT spans 0 to 18,446,744,073,709,551,615, an astronomically larger range.

To estimate how long an unsigned BIGINT would last if a company operated for 100 years, we compute the total seconds in 100 years and divide:

# BIGINT maximum value
max_bigint = 18446744073709551615
# Seconds in 100 years
seconds_in_100_years = 365 * 24 * 60 * 60 * 100
result = max_bigint / seconds_in_100_years
print(result)  # 5,849,424,173.55072 inserts per second

This means an unsigned BIGINT can handle roughly 5.8 billion inserts per second for a century—far beyond any realistic workload.

Migrating from INT to BIGINT

If your current table uses INT for the auto‑increment column and you anticipate growth, you can alter the column type safely:

-- Create example table
CREATE TABLE orders (
    id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    order_data VARCHAR(255)
);

-- Verify structure
DESCRIBE orders;

-- Change column to BIGINT
ALTER TABLE orders MODIFY id BIGINT UNSIGNED AUTO_INCREMENT;

-- Verify change
DESCRIBE orders;

Precautions

Back up your data before altering the table to prevent accidental loss.

Be aware that the ALTER operation may lock the table; perform it during low‑traffic periods.

If foreign keys reference the column, drop those constraints first, modify the column, then re‑add the constraints.

In summary, INT is sufficient for most scenarios, but when you need a larger numeric range, switching to BIGINT eliminates concerns about running out of IDs—unless your business itself outlives a century.