Add / Subtract Days from a Date
Find the date that is N days before or after any starting date. Optionally skip weekends to count only business days — essential for invoice terms, contract deadlines, and project planning.
How It Works
Adding or subtracting days from a date is one of the most common date calculations in business. Invoice terms ("net 30"), legal deadlines, project milestones, and subscription renewals all involve moving a specific number of days from a starting date.
Calendar days: The straightforward case. Add N to the day number. JavaScript's Date object handles month boundaries and leap year crossings automatically: if you start on January 28 and add 5 days, it correctly returns February 2 (or February 3 in a leap year).
Business days (skip weekends): This requires a loop. Starting from the base date, advance one day at a time, incrementing the business-day counter only on weekdays (Monday–Friday). Continue until the counter reaches the target number.
Worked example — calendar days: Start date 15 March 2025, add 90 days.
March has 31 days, so remaining in March = 16 days (days 16–31). 90 − 16 = 74 days remaining after March 31.
April: 30 days. 74 − 30 = 44 days remaining.
May: 31 days. 44 − 31 = 13 days remaining.
Answer: 13 June 2025 (which is a Friday).
Worked example — business days: Start 1 April 2025 (Tuesday), add 30 business days.
Week 1 (Apr 1–4): 4 days (the week has Mon–Fri but we start Tue). Running total: 4.
Each subsequent full week adds 5. After 5 more weeks (Apr 7–May 9): total = 4 + 25 = 29 days.
One more business day from May 9 (Friday) = May 12 (Monday).
Answer: 12 May 2025.
The "days until/since today" figure tells you whether the result is in the past or future, and by how many calendar days, which is useful for displaying a countdown or flagging overdue deadlines.
Frequently Asked Questions
What does "net 30" mean in business terms?
"Net 30" means payment is due 30 calendar days from the invoice date. So an invoice dated June 1 is due June 30 (since June has 30 days, +30 days = July 1 — actually this is a common point of confusion: net 30 from June 1 = July 1). Use this tool to calculate the exact due date for any net-30, net-60, or net-90 invoice.
Does the calculator account for public holidays?
The business-day mode skips only Saturday and Sunday. It does not account for public holidays, which vary by country and region. If your calculation requires skipping specific holidays, you will need to add extra days manually.
How do I find a date 6 months from today?
Use the date-difference calculator in reverse, or use the Add Days tool and estimate months as 30.44 days each. For exact month arithmetic (e.g., exactly 6 calendar months), use the "add months" mode which accounts for varying month lengths.
What if I subtract more days than are in the current year?
The calculator handles this correctly, rolling back across year boundaries and through multiple years if needed. Subtract 1,000 days from today and you'll get the correct date roughly 2 years and 9 months in the past.
Why does my result differ from what I counted manually?
Check whether you are counting the start date itself. By convention, "add N days to date X" moves N days forward from X, so X + 1 day = the next day (not X itself). If your manual count included the start date, subtract 1 from your day count.