Date Calculator
Calculate date differences or add and subtract days in your browser.
Date Calculator — what it does
Two calculations in one place: the number of days between any two dates, and the date that results from adding or subtracting a number of days from a starting point. Both walk the real calendar, so month lengths and leap years are respected, which mental arithmetic across month boundaries rarely manages.
When this tool helps
- Finding a deadline that is a fixed number of days after a contract signing or an order date.
- Counting the days between an invoice date and today to see how overdue it is.
- Working out return-window or warranty end dates from a purchase date.
How to use it
- Choose the mode: date difference, or add and subtract days.
- For a difference, enter the start and end dates.
- For addition, enter the start date and the number of days, negative to go backwards.
- Read the resulting count or date.
Accuracy, limits, and good practice
- This counts calendar days including weekends; when a deadline is defined in working days, use the business days calculator instead.
- Adding days lands on whatever weekday it lands on — check the result against a calendar if the outcome must be a working day.
- The difference between a date and itself is zero; agree whether your process counts the first day before comparing results with someone else.
Frequently asked questions
Can I subtract days?
Yes. Enter a negative number in add mode, and the calculator steps backwards through the calendar.
Does it handle months and years too?
The units here are days. For an age-style breakdown in years, months and days, the age calculator does that decomposition.
Why does my result differ from a spreadsheet?
Spreadsheets differ in whether they count end dates inclusively. This tool counts the days strictly between the two dates you entered.
Related tools on this site
- PDF Header & Footer — Add page-aware header or footer text
- Reorder PDF Pages — Create a new PDF using any custom page order
- Text Case Converter — Uppercase, lowercase, title case
Everything above runs inside this page. Date Calculator needs no account, no upload, and no server round trip — close the tab and nothing is left behind.
日期計算器能做什麼
兩種計算集中在一處：任意兩個日期之間相隔幾天，以及從某個日期加上或減去若干天後落在哪一天。兩者都沿真實日曆逐日推進，月份長短與閏年都有顧到，這正是跨月心算最容易失手的地方。
什麼時候用得上
- 找出簽約日或下單日之後固定天數的截止日。
- 計算發票日期與今天相隔幾天，看逾期多久。
- 從購買日推算退貨期限或保固到期日。
使用步驟
- 選擇模式：日期差，或加減天數。
- 算日期差時，輸入起訖兩個日期。
- 算加減時，輸入起始日期與天數，負數代表往回推。
- 查看得到的天數或日期。
精確度、限制與實務建議
- 此處計的是含週末的日曆天；若期限以工作天定義，請改用工作日計算器。
- 加天數後落在哪個星期幾就是哪天；若結果必須是工作日，請再對照月曆確認。
- 同一天與自己相差為零天；與他人核對前，先講好流程是否把第一天算進去。
常見問題
可以減天數嗎？
可以。在加減模式輸入負數，計算器就會沿日曆往回推。
也能以月或年計算嗎？
此工具以天為單位。若需要年、月、日形式的拆解，年齡計算器提供這種分解。
為什麼結果和試算表不一樣？
各試算表對是否包含結束日的定義不一；本工具計的是兩個日期之間的嚴格天數。
本站相關工具
- PDF 頁眉與頁尾 — 加入支援頁碼變數的頁眉或頁尾
- 重新排列 PDF 頁面 — 依自訂頁面順序建立新的 PDF
- 文字大小寫轉換 — 轉換大寫、小寫與標題格式
以上步驟全部在這個頁面內完成，日期計算器 不需要註冊、不上傳檔案、也不經過伺服器，關閉分頁後不會留下任何資料。