What this calculator does
The Investment Inflation Calculator shows how inflation erodes the buying power of an investment that earns compound interest and may also receive regular deposits or withdrawals. It runs in two modes. In "The Return on an Investment" you enter an initial investment (present value) and it returns both the nominal future value and that value expressed in today's dollars. In "Investment Required for a Target Return" you enter a goal stated in today's purchasing power and it computes the initial investment you need now. The math is universal time-value-of-money; the currency symbol is illustrative.
How to use it
Pick a mode, then enter the dollar amount, the number of years, the annual interest rate, how often interest compounds, and the expected inflation rate. Optionally add a recurring deposit or withdrawal and choose its frequency. The tool aligns payment frequency with compounding by deriving an equivalent rate per payment period, so weekly deposits with monthly compounding are handled correctly.
The formula explained
The lump sum grows by FV = PV(1 + r/m)^{mt}, where r is the annual rate, m is compoundings per year and t is years. Periodic payments form an ordinary annuity valued with an equivalent payment-period rate r_{pay} = (1 + r/m)^{m/q} - 1 over N = q · t payments. Deposits add and withdrawals subtract. Finally the nominal total is deflated by (1 + i)^{t} to express it in today's dollars.
Worked example
Goal mode, target 100,000 in today's dollars, 10 years, 6.25% rate compounded monthly, 2.25% inflation, no payments. Nominal target
使用注意事項與精準校對原則（6 大核心守則）
📐 1. 嚴格對齊輸入量綱與單位
輸入各項數值時請務必確認量綱（例如小時、天數、金額、百分比），避免單位不匹配引發推算偏差。
🔒 2. 純前端本機毫秒級隱私保障
所有計算邏輯 100% 在您的終端瀏覽器內完成，資料絕不上傳伺服器，嚴格守護商業與個人隱私。
📊 3. 符合公認學術與產業計算模型
演算法嚴格遵循國際通用數學公式與標準計算模型，經多重情境交叉核對，數值嚴密精確。
📋 4. 一鍵複製與免登入 PDF 匯出
支援一鍵複製推算結果字串至剪貼簿，亦可直接點擊列印按鈕輸出純淨 PDF 工作報表。
🔄 5. 多情景敏感度動態對比
建議針對極端值與多組預期情景分別試算，觀察輸出數據的波動區間，輔助做出更穩健的決策。
🛡️ 6. 專業諮詢與日常參考免責聲明
本工具運算結果供日常排程、學業研習與事前參考之用，如涉及重大法規或投資決策請諮詢持證專家。