Reference implementation for elapsed-day and elapsed-month calculations, including leap year handling
Methodology: Days Since = End Date − Start Date (in milliseconds ÷ 86,400,000). Weeks = Days ÷ 7 (rounded down). Approximate months = Days ÷ 30.4375 (average days per month accounting for leap years). Years use exact calendar month counting for precision. Leap years are handled automatically by JavaScript’s native Date object.
⏱ Last reviewed: April 2026
How to Calculate Days Since a Date
Counting the number of days that have passed since a specific date is one of the most common time calculations people need. Whether you’re tracking sobriety milestones, measuring how long since an event occurred, calculating warranty periods, or just satisfying curiosity, the math is straightforward — but doing it by hand across months and years requires careful attention to leap years and varying month lengths.
The Days Since Formula
Days Since = End Date − Start Date
Example: Today is April 6, 2026 and your past date is January 1, 2026.
Days Since = April 6, 2026 − January 1, 2026 = 95 days
Weeks = 95 ÷ 7 = 13 weeks, 4 days
Months ≈ 95 ÷ 30.44 = approximately 3.1 months
Days Since vs. Days Between
Both calculations measure elapsed time, but days since specifically counts from a past date to today (or another specified end date), while days between counts the span between any two arbitrary dates. This calculator handles both: leave the end date blank to count to today, or enter an end date to count between two specific dates.
Handling Leap Years
A leap year occurs every 4 years (with exceptions for century years not divisible by 400). This adds one extra day — February 29 — to the calendar. When your date range spans one or more leap years, the calculator automatically accounts for the extra day. For example, the span from January 1, 2024 to January 1, 2025 is 366 days, not 365, because 2024 is a leap year.
Common Uses for Days Since Calculator
Sobriety tracking — counting days, weeks, and months of recovery milestones
Anniversary countdowns — how many days since a wedding, first date, or memorial
Legal deadlines — statute of limitations periods measured from incident date
Warranty periods — days since purchase to determine coverage eligibility
Project tracking — how many days a project has been running
Medical monitoring — days since a diagnosis, surgery, or last test
Employment records — days since hire date or performance review
Age in days — exact number of days lived since birth date
Days Since Reference Table
Time Period
Approx. Days
Exact Notes
1 week ago
7
Always exactly 7 days
1 month ago
28–31
Varies by month length
3 months ago
90–92
Depends on which months
6 months ago
181–184
Leap year adds 1 day
1 year ago
365 or 366
366 if leap year
2 years ago
730 or 731
731 if period includes a leap year
5 years ago
1,826 or 1,827
Typically includes 1–2 leap years
10 years ago
3,652 or 3,653
Typically includes 2–3 leap years
💡 Tip: To count days since a date inclusively (counting both the start day and today), add 1 to the result. The calculator shows the exclusive count by default, which is the standard for measuring elapsed time — the same method banks use for interest accrual and courts use for legal deadlines.
How to Calculate Days Since in Excel or Google Sheets
In Excel or Google Sheets, you can calculate days since a date with a simple formula. If your past date is in cell A1, enter =TODAY()-A1 and format the result as a number. This gives the number of days between A1 and today. You can also use =DAYS(TODAY(),A1) for the same result. To convert to weeks, divide by 7: =INT((TODAY()-A1)/7).
Days Since in Programming
In JavaScript: Math.floor((Date.now() - new Date(pastDate)) / 86400000). In Python: (date.today() - past_date).days. In SQL: DATEDIFF(CURDATE(), past_date) (MySQL) or CURRENT_DATE - past_date (PostgreSQL). All approaches work identically to this calculator for any date range within the Gregorian calendar system.
Frequently Asked Questions
Subtract the past date from today’s date. Days Since = Today − Past Date. For example, January 1, 2026 to April 6, 2026 is 95 days. This calculator handles the subtraction automatically, including leap years and varying month lengths.
From January 1, 2026 to April 6, 2026 is 95 days, 13 weeks and 4 days, approximately 3.1 months. Enter January 1, 2026 in the calculator above to get the exact count updated to today’s date.
Yes. To include today in the count, add 1 to the result. For example, if 95 days have elapsed since January 1, 2026, the inclusive count (counting both January 1 and April 6) is 96 days. The calculator shows exclusive elapsed days by default, which is the standard for measuring time spans.
Days since and days ago mean exactly the same thing. Both describe the number of calendar days that have elapsed between a past date and today. “30 days ago” is the same as saying “30 days have passed since” that date.
In Excel, use =TODAY()-A1 where A1 contains your past date, then format the result cell as a number. You can also use =DAYS(TODAY(),A1). To get weeks, use =INT((TODAY()-A1)/7). Google Sheets uses the same formulas. These are equivalent to what this calculator computes.
Enter your date of birth in the calculator above to find your exact age in days. A person born January 1, 1990 has lived approximately 13,244 days as of April 6, 2026. The exact count depends on how many leap years fall within the period.
Yes. Leap years are handled automatically. When your date range includes February 29 of a leap year, that day is counted. For example, the period from January 1, 2024 to January 1, 2025 is 366 days, not 365, because 2024 is a leap year.
Divide the number of elapsed days by 7. Weeks = Days Since ÷ 7. If 98 days have passed, that is exactly 14 weeks. The Days Since Calculator shows weeks automatically in the results, along with any remaining days.
No. The Days Since Calculator is for past dates only. If you need to count days until a future event, use a Days Until Calculator instead. Entering a future date would produce a negative number, which has no meaningful interpretation for elapsed time.
To get an approximate month count, divide the elapsed days by 30.44 (the average days per month including leap years). For exact calendar months, count the months directly. The calculator shows both an approximate decimal month count and the exact day breakdown in its results.
Common uses include sobriety milestone tracking, anniversary calculations, legal statute of limitations deadlines, warranty period checks, project duration tracking, medical monitoring intervals, employment records, and calculating your exact age in days. Many people use it simply to quantify how long ago a memorable event occurred.
From January 1, 2026 to April 6, 2026 is 95 days. Enter January 1, 2026 in the calculator to get today’s exact count. New Year’s Day is a common reference point for “days since” queries because it marks the start of the calendar year.
In JavaScript: Math.floor((Date.now() - new Date(pastDate)) / 86400000). This subtracts the past date’s millisecond timestamp from the current timestamp, then divides by 86,400,000 (milliseconds in one day) and rounds down to get whole days.