Processed entirely on your device — nothing is uploaded
How to use the add days to a date
- 1Pick the start date — it defaults to today.
- 2Choose add or subtract, enter the count, and pick days, weeks or calendar months.
- 3Read the resulting date and its weekday.
- 4For month-based periods, note the calendar-month behaviour explained below — it differs from adding 30 days.
Days versus calendar months — the difference that bites
Adding 30 days and adding one calendar month agree only in four months of the year. A 90-day period from March 15th ends June 13th; a 3-month period ends June 15th. Contracts use both conventions freely, which is why this tool offers both units instead of pretending they are interchangeable — pick the one your document actually says.
Month arithmetic has one famous edge: a month after January 31st. There is no February 31st, so the result rolls into early March — the standard JavaScript behaviour, and also what most legal drafting conventions produce. If your document says 'the corresponding day of the following month, or the last day if none', compute accordingly.
Subtraction mirrors addition exactly, which makes the tool a back-scheduler: if a submission is due on a fixed date and the courier needs 12 days, subtracting finds the real deadline — the one your calendar should show.
The weekday is half the answer
The result shows its weekday because dates without weekdays cause the second round of arithmetic: a 60-day payment window that ends on a Saturday effectively ends Friday or Monday, depending on the convention, and a court filing landing on a gazetted holiday moves to the next working day under the General Clauses Act.
This tool deliberately does not skip weekends or holidays for you — 'business days' definitions vary by industry, state and contract, and silently applying one would produce confidently wrong dates. It gives the exact calendar date; you apply your context's working-day rule to it.
For recurring deadlines — rent on the 5th, EMI on the 7th, quarterly filings — the month unit with a fixed start date reproduces the whole series one hop at a time.
The everyday cases
The searches that lead here are wonderfully concrete: when does my 90-day probation end, what date is 45 days before the wedding, when does a 180-day visa window close, what was the date 100 days ago. Each is one subtraction or addition with the right unit — and each is exactly the kind of count that mental arithmetic fumbles across month boundaries.
Medical and pharmacy schedules use it too: a 28-day prescription cycle, a follow-up 'in six weeks', a vaccination due 84 days after the first dose. The weeks unit exists precisely for these.
Everything runs in your browser; dates are never transmitted, and the page keeps working offline once loaded. Pair this page with the Date Difference Calculator — one finds the end of a period, the other measures a period that already exists — and between the two of them, every deadline question reduces to a couple of clicks.
Frequently asked questions
What date is 90 days from today?
Leave the start date on today, enter 90 days, and read the result with its weekday. The count is exact calendar days, leap days included.
Is adding 3 months the same as adding 90 days?
No — three calendar months span 89 to 92 days depending on the start date. The tool offers both units so you can match whichever your document specifies.
What happens a month after the 31st?
When the target month has no such day, the date rolls forward into the next month (January 31st + 1 month lands in early March) — the standard convention. Documents sometimes specify 'last day of the month' instead; check yours.
Does it skip weekends or holidays?
Deliberately not — business-day rules differ by contract and jurisdiction. It gives the exact calendar date and shows the weekday so you can apply your own rule.
Is anything I enter stored?
No — the computation is local to your browser and nothing is uploaded.