Days Since & Days Until Calculator
Count the days since a past date or until a future one — plus weeks, months and hours. Also works as a days-between-two-dates calculator. Free, no signup.
A past date counts up (quit date, start date, streak). A future date counts down (deadline, race, event).
How the day count is calculated
The tool reads both dates as plain calendar dates in the ISO 8601 YYYY-MM-DD form your browser's date picker produces, pins each to local midnight, and takes the difference. That difference is exclusive: the gap from the 1st to the 2nd is one day. Leap days come along for free because the comparison runs on the proleptic Gregorian calendar your device already uses — 2024 and 2028 contribute a 29th of February, 1900 and 2100 do not.
Weeks are the day total divided by 7, shown as whole weeks plus the leftover days. Hours are whole days × 24. Months get two answers on purpose: a calendar-accurate years, months, days walk, and a decimal figure using the Gregorian mean month of 30.4375 days (365.25 ÷ 12). Long-range date arithmetic almost always disagrees slightly between those two methods, so both are on screen rather than one being quietly picked for you.
Days since, days until, days between
One date answers two questions. A date in the past gives a days since count — the day you quit drinking, the day you started running, the day the streak began. A date in the future gives days until — the race, the exam, the deadline you are building toward. Switch on the second date field and the same subtraction answers the plain days between two dates question with today taken out of the picture entirely.
Why a running day count changes behaviour
A number you have built up is a number you do not want to reset. That reluctance is ordinary loss aversion, and it is one of the most dependable levers in behaviour change — it is the same mechanism behind consistency streaks and behind the stubbornly popular "don't break the chain" method. Working out how long a habit actually takes to shift is a separate question, covered in how long it takes to break a habit.
The catch with a calculator is that it only tells you the number once. If you want the count to keep itself, log the habit as a daily check-in in HabitBox — the streak updates every time you tap, it works on iOS and Android, needs no account, and keeps the data on your device.
Note: all dates are interpreted in your device's local time zone and nothing is sent anywhere — the entire calculation runs in your browser.
Frequently asked questions
How do I calculate the number of days between two dates?+
Subtract the earlier calendar date from the later one and count whole days. This calculator does it for you: pick a date and it shows the days since (if it's in the past) or days until (if it's in the future). Turn on the second date field to measure the gap between any two dates instead of using today.
Does the result include the start day or the end day?+
Neither end is double-counted — the number is the exclusive difference between the two calendar dates. January 1 to January 2 is 1 day, not 2. If you're counting a streak where the first day itself counts as day one, add 1 to the total.
Why doesn't the month count match days divided by 30?+
Months aren't equal length. The 'years, months, days' line walks the actual calendar (a February-to-March step is 28 or 29 days, an April-to-May step is 30). The decimal months figure uses the Gregorian mean month of 30.4375 days, so the two can differ by a day or two — both are correct, they answer slightly different questions.
How do I count the days since I quit something?+
Set the date picker to your quit date and read the big number: that's your current streak in days. The milestone strip shows the 7, 30, 100, and 365-day marks and exactly how many days you are from the next one.
Does it handle leap years and daylight saving time?+
Yes. Dates are compared as calendar dates in your device's local time zone, so leap days are included automatically and a daylight-saving shift (a 23 or 25-hour day) never adds or removes a day from the count. The hours figure is whole days multiplied by 24.
Keep the count going in HabitBox
A calculator gives you the number once. HabitBox keeps it — log a one-tap check-in each day, watch the streak climb past 7, 30 and 100 days, and see it on your home screen. iOS and Android, no account needed, data stays on your device.
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