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Compound Interest Calculator

Project how a starting amount and optional monthly contributions grow over time under compound interest. Choose the compounding frequency — from daily to continuous — and see the year-by-year balance, total contributions, and interest earned.

ツール要約

このツールは構造化された入力を受け取り、サーバーへアップロードせずにブラウザで決定的な出力を返します。

ツール名
Compound Interest Calculator
入力の目的
変換・検証・分析するソースコンテンツを入力してください。
出力の目的
コピー・再利用・デバッグに適した正規化された出力を受け取ります。
入力例
$10,000 · 7% · 20 years · monthly · no contributions
出力例
Future value ≈ $40,387 · Interest ≈ $30,387
Future value
$20,096.61
Contributions
$10,000.00
Interest earned
$10,096.61
YearContributionsInterestBalance
Year 1$10,000.00$722.90$10,722.90
Year 2$10,000.00$1,498.06$11,498.06
Year 3$10,000.00$2,329.26$12,329.26
Year 4$10,000.00$3,220.54$13,220.54
Year 5$10,000.00$4,176.25$14,176.25
Year 6$10,000.00$5,201.06$15,201.06
Year 7$10,000.00$6,299.94$16,299.94
Year 8$10,000.00$7,478.26$17,478.26
Year 9$10,000.00$8,741.77$18,741.77
Year 10$10,000.00$10,096.61$20,096.61

Uses the compound interest formula A = P(1 + r/n)^(nt) — or A = Pe^(rt) for continuous compounding — with monthly contributions distributed across periods. Investment returns vary; this is a deterministic projection, not a guarantee.

ツールの紹介

Project how a starting amount and optional monthly contributions grow over time under compound interest. Choose the compounding frequency — from daily to continuous — and see the year-by-year balance, total contributions, and interest earned.

ツール概要

Compound interest is interest that earns interest: each period, the balance is multiplied by 1 + r/n (or e^(r/n) in the continuous limit), so growth is exponential rather than linear. This calculator treats principal plus optional regular contributions the same way a savings account, fixed deposit, SIP, or index-fund projection would. Results are deterministic — real investment returns fluctuate — so treat the output as a planning estimate, not a guarantee.

ユースケース

  • Plan a retirement, emergency-fund, or down-payment target
  • Compare a lump-sum investment to a systematic monthly plan
  • Estimate future value of a fixed deposit or index fund
  • Quantify how compounding frequency changes the final balance

入力／出力の例

入力の目的
$10,000 · 7% · 20 years · monthly · no contributions
出力の目的
Future value ≈ $40,387 · Interest ≈ $30,387
入力の目的
$0 · 8% · 30 years · monthly · $500/month
出力の目的
Future value ≈ $745,180 · Contributions $180,000 · Interest ≈ $565,180

よくある質問

What is the compound interest formula?+
A = P · (1 + r/n)^(n·t), where P is principal, r is the annual rate, n is the number of compounding periods per year, and t is time in years. For continuous compounding the formula is A = P · e^(r·t).
How are monthly contributions handled?+
Contributions are converted to a per-period amount (for example, $500/month becomes $1,500/quarter when compounding is quarterly) and added at the end of each period before the next compounding step.
Is this a SIP (Systematic Investment Plan) calculator?+
Yes — use the monthly-contribution field and pick monthly compounding to model a typical SIP at an assumed annualized return.
Does compounding frequency matter much?+
At typical savings rates the difference between daily and continuous compounding is small, but over long horizons or higher rates it is noticeable. Try the same inputs across frequencies to see the gap.

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