Five date questions, one calculator
Almost every date question people actually ask boils down to one of five shapes: how far apart are two dates, what date do I land on if I add or subtract some time, how long ago (or how soon) is a specific date, and what day of the week does a date fall on. This tool covers all five without needing five separate pages.
Sota el capó, cada mode utilitza la mateixa aritmètica conscient del calendari: la mateixa biblioteca que gestiona correctament els anys de traspàs, els mesos de durada diferent i el total de dies des d'un punt de referència fix.
How the difference between two dates is calculated
Counting the raw number of days between two dates is simple subtraction once both are converted to a single running day count. Expressing that gap as years, months, and days is the harder part, since it has to account for variable month lengths and leap years rather than assuming every month is 30 days.
Worked example: from March 10 to July 20 of the same year. That's 4 months and 10 days apart, or 132 days total. Across a year boundary it works the same way — January 15, 2026 to March 1, 2027 comes out to 1 year, 1 month, and 14 days, or 410 days total.
Adding or subtracting time from a date: the month-end trap
Adding a fixed number of days is straightforward. Adding months or years is not, because "one month later" doesn't always land on a real date — there's no April 31 or February 30.
The convention this calculator follows: adding one month to January 31 lands on February 28 in a normal year, or February 29 in a leap year — the calendar's actual last day of February, rather than overflowing into March. Adding a year to February 29 on a leap year similarly resolves to February 28 the following year, since that date doesn't exist outside leap years.
This clamp-to-month-end behavior is the most common convention, but it's not the only one some tools use — a few systems instead roll the extra days into the next month. If you're matching a specific system's date math (a billing cycle, a legal contract), it's worth confirming which rule that system follows.
Business days vs. calendar days
A calendar day count includes every day, weekends included. A business day count only counts Monday through Friday, which is what most shipping estimates, contract deadlines, and processing times are actually quoted in — a "5 business day" turnaround starting on a Thursday finishes the following Thursday, not the following Tuesday.
Una limitació honesta que val la pena assenyalar: el recompte de dies laborables d'aquesta calculadora només exclou els caps de setmana, no els festius. Els calendaris de vacances difereixen segons el país i sovint segons l'estat, la indústria o l'empresa, de manera que una eina genèrica no pot endevinar amb seguretat quins s'apliquen a la vostra situació; si un dia festiu entra dins del vostre interval de dates, resteu-lo manualment del total.
Where this kind of date math actually gets used
- Contract and legal deadlines defined as "N days from signing" or "N business days from notice."
- Project planning — working backward from a launch date to figure out when a task needs to start.
- Cicles de facturació i subscripció que renoven un interval fix després de la data de l'últim pagament.
- Planificació de viatges i visats, on les estades permeses sovint es limiten a un nombre determinat de dies.
- Simple curiosity — what day of the week does a specific historical or future date fall on.
Si el que realment necessiteu és una edat precisa en anys, mesos i dies a partir d'una data de naixement en lloc d'un interval general entre dues dates arbitràries, el Calculadora d'edat is built specifically for that, with zodiac signs and milestone tracking built in. For a running count of days between two dates without the year/month breakdown, the Comptador de dies gets straight to that number.