Compound Interest Calculator
Estimate future value with compounding and regular contributions
Compound Interest Calculator — what it does
Enter a starting principal, an annual rate, a term in years, how many times interest compounds each year and any recurring contribution, and the calculator projects the future value alongside how much you contributed and how much came from interest. Separating those two figures is what makes the effect of compounding visible rather than abstract.
When this tool helps
- Projecting a savings plan or retirement account where a fixed amount goes in every month.
- Comparing two deposit products whose rates look similar but compound monthly versus annually.
- Showing a realistic long-run picture before deciding between paying down debt and investing.
How to use it
- Enter the starting principal and the annual interest rate.
- Set the number of years and compounds per year.
- Add a contribution amount for each period if you make one.
- Calculate to see future value, total contributed and interest earned.
Accuracy, limits, and good practice
- The rate is nominal, not inflation-adjusted. Subtract expected inflation to see what the balance is worth in today's money.
- Compounding frequency matters less than people expect: monthly versus annual at 5 percent differs by only about 0.11 percentage points of effective yield.
- Real accounts have fees, taxes on interest and variable rates. Treat the projection as a clean-room model, not a promise.
Frequently asked questions
When are contributions added?
Once per compounding period, alongside the interest calculation, which matches how most regular savings plans actually work.
What is the rule of 72?
Divide 72 by the annual rate for a rough doubling time. At 6 percent, money roughly doubles in twelve years — close enough for mental arithmetic.
Can I model an investment that loses money?
Enter a negative rate. The projection then shows compounding decline, which is the correct arithmetic for a sustained loss.
Related tools on this site
- Inventory EOQ & Reorder Calculator — Calculate EOQ, reorder point, annual orders, and order cycle
- Salary Converter — Convert hourly, weekly, monthly, and annual compensation values
- Work Hours Calculator — Calculate paid hours, break time, and estimated pay
Everything above runs inside this page. Compound Interest Calculator needs no account, no upload, and no server round trip — close the tab and nothing is left behind.
複利計算器能做什麼
輸入本金、年利率、年期、每年複利次數與每期投入金額，計算器會推算未來價值，同時分列你總共投入多少、利息又貢獻多少。把這兩個數字拆開，複利的效果才會從抽象概念變成看得見的金額。
什麼時候用得上
- 推算每月固定扣款的儲蓄計畫或退休帳戶。
- 比較兩張利率相近、但一個按月複利、一個按年複利的存款商品。
- 在「先還債還是先投資」的決策前，看清長期的實際樣貌。
使用步驟
- 輸入本金與年利率。
- 設定年期與每年複利次數。
- 若有定期投入，填入每期金額。
- 計算後查看未來價值、累積投入與利息收益。
精確度、限制與實務建議
- 利率為名目利率，未扣通膨。想知道以今日購買力計算的價值，需自行減去預期通膨率。
- 複利頻率的影響比想像中小：5% 之下按月與按年複利的實質年利率僅差約 0.11 個百分點。
- 真實帳戶還有手續費、利息稅與浮動利率，這份推算是理想模型，不是保證。
常見問題
定期投入是在什麼時候計入？
每個複利期各計入一次，與利息一起計算，這與多數定期定額計畫的實際運作方式相符。
什麼是 72 法則？
用 72 除以年利率可粗估翻倍所需年數。6% 之下約十二年翻倍，作為心算已經夠準。
可以模擬會虧損的投資嗎？
把利率填成負數即可，推算會顯示複合式的衰退，這正是持續虧損的正確算法。
本站相關工具
- 庫存 EOQ 與補貨點計算器 — 計算經濟訂購量、補貨點、年度訂購次數與週期
- 薪資換算器 — 在時薪、週薪、月薪與年薪之間進行換算
- 工時計算器 — 計算實際工時、休息時間與預估薪資
以上步驟全部在這個頁面內完成，複利計算器 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。