Calculator Use
The days since calculator is a specialized tool designed to provide an exact count of calendar days between two points in time. Whether you are tracking a personal milestone, monitoring a project deadline, or calculating historical durations, this tool eliminates the manual error associated with leap years and varying month lengths.
You can use this calculator in two primary modes: calculating the time elapsed from a past date until today, or calculating the span between two specific dates in history or the future.
- Start Date
- The initial date from which you begin counting. For "Days Since" calculations, this is typically a past event like a birth date or anniversary.
- End Date
- The concluding date of your range. If calculating "until today," the system automatically uses your current local date.
- Include End Date
- An optional setting that adds 1 day to the total, effectively counting both the start and end dates as full days (inclusive counting).
How It Works
Calculating the number of days between dates involves more than simple subtraction because the Gregorian calendar contains irregularities. This days since calculator uses a standardized time-conversion formula based on milliseconds since the Unix Epoch (January 1, 1970).
Total Days = (End Date Timestamp – Start Date Timestamp) / 86,400,000
- Timestamp: The numeric representation of a date in milliseconds.
- 86,400,000: The number of milliseconds in a standard 24-hour day (24 hours × 60 minutes × 60 seconds × 1,000 milliseconds).
- Leap Years: The calculator accounts for February 29th in years divisible by 4 (except for years divisible by 100 but not 400).
Calculation Example
Example: Suppose you want to find out how many days have passed since the beginning of the decade (January 1, 2020) until January 1, 2024.
Step-by-step solution:
- Start Date: January 1, 2020
- End Date: January 1, 2024
- Total Years: 4 years (2020, 2021, 2022, 2023)
- Leap Day Adjustment: 2020 was a leap year, adding 1 day.
- Calculation: (365 days × 4) + 1 leap day = 1,461 days.
- Result = 1,461 Days (or 1,462 if including the end date).
Common Questions
Does this calculator include leap years?
Yes. Our days since calculator automatically identifies leap years within your selected date range and adds the extra day (February 29) to the total count ensuring 100% accuracy for long-term spans.
What does "Include End Date" mean?
In standard date subtraction, the result is the difference (e.g., Friday minus Monday is 4 days). If you check "Include End Date," the calculator counts the starting day as Day 1 and the ending day as a full day, which is common in rental agreements or insurance policies.
Can I calculate days until a future date?
Yes. By using the "Days Between Two Dates" option, you can enter a future date as the End Date. The calculator will provide the total days remaining until that event occurs.