Article — 30 Day Calculator
30 day calculator: what date is 30 days from today?
A 30 day calculator adds or subtracts 30 days from any date. If today is May 13, 2026, then 30 days from now is June 12, 2026, a Friday. The number "30 days" shows up so often in contracts, returns, and grace periods that it has become one of the most-searched calendar queries on the web.
The calculator at the top of this page handles any number of days — 30, 60, 90, 365, or anything else — and can count forward or backward. It also supports business days (Monday through Friday only) for contracts that specify "business days" rather than calendar days.
What is 30 days from today?
If today is May 13, 2026, then 30 days from today is June 12, 2026 (Friday). Use the calculator above to compute 30 days from any other start date — change "Start date" to your reference date, leave the day count at 30, and read the result.
The math is simple addition: take the calendar date and walk forward 30 calendar days, handling month boundaries and leap years automatically. JavaScript, Excel, and SQL all expose date functions that do this, and so does this calculator. There is no daylight-saving complication because the calculation is in whole calendar days, not hours.
Calendar days vs. business days
The "30 days" in everyday speech almost always means 30 calendar days, weekends included. "30 business days" is a different unit: it skips Saturday and Sunday, and usually skips holidays too. The gap between them is large.
30 business days is 42 calendar days — almost half again as long. That difference catches people regularly. A "30 business day" return window is much longer than a "30 day" window. A "30 business day" payment term gives the customer six full weeks instead of four.
"30 days" and "30 business days" look similar but produce deadlines almost two weeks apart. US case law generally treats "days" without qualification as calendar days, so vague contracts default to the shorter interpretation. If you care which one applies, the contract must say so explicitly.
Why "30 days" shows up everywhere
30 days is a convenient unit. It is close enough to one month to feel monthly, but unambiguous in a way "one month" never is. Government rules, retailers, and contract templates have used it for so long that 30 days is the default for almost every soft deadline in modern life:
- Returns: Amazon, Walmart, and Target all use a 30-day return window for most items
- B2B invoices: NET 30 is the most common payment term in US business
- FMLA leave: employees must give 30 days' notice for foreseeable leave
- FTC Shipping Rule: online sellers must ship in 30 days or refund
- Insurance grace periods: typically 30 or 31 days
- J-1 visa exit: 30-day grace period after the program ends
- Employment notice: 30 days is the default in many countries' labor codes
- Money-back guarantees: the standard offer in consumer software and DTC
The word "month" comes from "moon," and the lunar cycle from new moon to new moon is 29.53 days. Ancient Babylonian calendars alternated 29-day and 30-day months to track the moon. The modern 30-day month survives in contracts and billing cycles because it is close enough to the lunar average to feel natural, but precise enough to settle disputes.
NET 30 and invoice due dates
NET 30 means the invoice is due 30 calendar days from the invoice date. It is the default payment term in US business-to-business commerce. An invoice dated May 13 with NET 30 terms is due June 12. The calculator above gives the same answer in one click.
Variations are common. NET 15 (two weeks) is used for small contractors who need faster cash. NET 45, NET 60, and NET 90 are common when the customer is a large enterprise with internal approval cycles that take longer than 30 days. "2/10 NET 30" means: full payment due in 30 days, or 2% discount if paid within 10 days. The discount math usually works out to an effective annualized rate around 36%, which is why most companies pay early when offered.
30 days vs. one month
30 days is exactly 30 days. One calendar month varies from 28 to 31 days. The distinction sounds pedantic but it changes deadlines.
30 days from February 1 is March 3 (or March 2 in a leap year). One month from February 1 is March 1. A two-day gap. In most contracts the wording matters because the courts will read it literally — if your contract says "30 days" you get 30 days, not "the same date next month."
The Federal Trade Commission's "Mail, Internet, or Telephone Order Merchandise Rule" requires online sellers to ship goods within 30 days of the order, or provide the customer with the option to cancel for a full refund. The rule has been in force since 1975 and the maximum civil penalty for violation is currently $50,120 per occurrence. That single rule is the legal floor for "ships within 30 days" promises across US e-commerce.
Counting 30 days backward
To count 30 days before a date, use the calculator's "Days before" toggle. Enter the target date as the start, set the day count to 30, and the result is the date 30 days earlier.
Example. 30 days before May 31 is May 1. 30 days before March 15 is February 13 in non-leap years, February 14 in leap years. 30 days before January 1 falls in early December of the previous year — December 2.
Backward counting matters for compliance deadlines that work from a known future date. Tax filings, court motions, lease renewals, and visa applications all have rules of the form "must be submitted at least N days before the event." Working backward from the event date is the standard way to plan.
When a 30-day deadline lands on a weekend
What happens when the 30th day is a Saturday or Sunday depends on the rules of the issuing body:
US federal courts and the IRS roll forward to the next business day. A tax deadline that falls on a Saturday becomes effective the following Monday. The same applies to most state-level filing rules.
Private contracts usually do not roll forward. If a contract says "due in 30 days" and the 30th day is a Sunday, the payment is due Sunday. Most companies will accept a Monday payment without dispute, but they are not required to. Read the contract — some include explicit "next business day" language, most do not.
If you are drafting a contract, decide which behavior you want and write it in. "30 days from the invoice date, with deadlines falling on weekends rolling to the next business day" removes a category of disputes. Silence on the question defaults to the harder reading — the calendar date is the deadline, weekend or not.
Common 30-day mistakes
Assuming "30 days" means "one month." Close, but not equal. 30 days lands on different calendar dates than "one month" depending on which month you start in. For contracts and tax deadlines, use the exact day count.
Forgetting that "business days" is much longer. 30 business days is 42 calendar days. People plan for one month and lose two weeks.
Counting the start date. "30 days from today" usually excludes today itself. The result is the 30th day after, not the 30th day starting from today. The calculator above follows this convention.
Ignoring time zones. "30 days from January 31 at 11pm Pacific" lands in February or March 1 depending on which timezone you are in when the deadline arrives. For legal deadlines, the timezone of the receiving party usually governs.
Visa renewals, tax filings, and court motions almost always reward early submission. Last-day filings expose you to weekend rules, timezone disputes, server outages, and human error. If a deadline matters, build a one-week buffer.