How do you add days or hours to a Unix timestamp?

Because a Unix timestamp is simply a count of seconds, adding time is straightforward: multiply your interval into seconds and add it to your timestamp. For example, to add 5 days: New Timestamp = Current Timestamp + (5 * 86,400).

How do you calculate expiration timestamps for JWT or sessions?

To create an expiration timestamp (such as a 15-minute JWT exp claim), add the duration in seconds to the current Unix time: Math.floor(Date.now() / 1000) + (15 * 60).

Unix Epoch Calculator - Add & Subtract Time from Timestamps

How Unix Timestamp Arithmetic Works

One of the greatest advantages of using Unix timestamps in software engineering is that temporal math is reduced to simple integer addition and subtraction. Instead of juggling complex calendar rules, leap days, and timezones, you can calculate offsets using fixed constant intervals:

1 Minute60s

1 Hour3,600s

1 Day86,400s

1 Week604,800s

Timestamp Calculation in Code (JavaScript, Python, SQL)

JavaScript / TypeScriptCalculating Expirations & Future Epochs

const currentEpoch = Math.floor(Date.now() / 1000);

// Add 7 days
const sevenDaysLater = currentEpoch + (7 * 86400);

// Add 30 minutes (e.g. auth token expiry)
const tokenExpiry = currentEpoch + (30 * 60);

// Subtract 24 hours
const yesterdayEpoch = currentEpoch - 86400;

Python 3datetime.timedelta

import time
from datetime import datetime, timedelta, timezone

current_epoch = int(time.time())

# Direct integer arithmetic
future_epoch = current_epoch + (14 * 86400) # +14 days

# Or using datetime and timedelta for calendar accurate math
dt = datetime.now(timezone.utc) + timedelta(days=14, hours=2)
print("Calculated Epoch:", int(dt.timestamp()))

SQL (PostgreSQL & MySQL)Interval Arithmetic

-- PostgreSQL:
SELECT to_timestamp(1730123456) + INTERVAL '30 days';

-- MySQL:
SELECT DATE_ADD(FROM_UNIXTIME(1730123456), INTERVAL 30 DAY);

The Year 2038 Problem (Y2K38 Limit)

When performing calculations far into the future, be mindful of the Year 2038 boundary. On January 19, 2038 at 03:14:07 UTC, signed 32-bit integer Unix timestamps will overflow past 2,147,483,647. Always ensure your database columns and application runtimes use signed 64-bit integers (BIGINT in SQL), which remain safe for over 292 billion years.

Explore Related Utilities

Timestamp Difference

Calculate the duration between two timestamps.

Epoch to Date Converter

Convert calculated timestamps into formatted dates.

Current Unix Timestamp

View current live seconds to use as a baseline.