# Inflation calculator (future cost and purchasing power)

> Calculate what a purchase will cost after inflation, what your money will still buy, and your real return after inflation.

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분야: 금융 계산기

Inflation raises prices by a percentage each year, and it compounds like interest. At a steady rate π, a purchase costing A today costs A(1 + π)^n after n years, and cash held for n years buys only A ÷ (1 + π)^n of today's goods. The real return on savings follows Irving Fisher's relation: (1 + nominal rate) ÷ (1 + inflation) − 1.

With the defaults, 1,000 and 3% inflation for 10 years, the same purchase will cost 1,343.92 and cash of 1,000 will buy 744.09 of today's goods, a 25.59% loss of purchasing power. Savings earning 6% have a real return of 2.9126% a year, not 3%, and grow to 1,332.56 in today's money.

The inflation rate is held constant. Official price indices such as the US CPI-U move unevenly and differ by basket and country, so for past prices use the index values themselves, for example through the BLS CPI inflation calculator.

## 입력

- **Amount today**
- **Inflation rate (per year)**
- **년**
- **Return on savings (per year)**: Used for the real return; enter 0 for cash kept at home

## 결과

- Future cost of the same purchase — 주요 결과
- What the amount will buy, in today's money
- Purchasing power lost
- Total price rise
- Real return (per year)
- Savings at that return, in today's money

## 공식

$$
\text{Future cost} = A(1+\pi)^{n},\quad \text{Purchasing power} = \frac{A}{(1+\pi)^{n}},\quad r_{\text{real}} = \frac{1+i}{1+\pi} - 1
$$

## 계산 예제

### 1,000 at 3% inflation for 10 years, savings at 6%

- Amount today: 1000
- Inflation rate (per year): 3%
- 년: 10
- Return on savings (per year): 6%
- **Future cost of the same purchase: 1,343.92**
- **What the amount will buy, in today's money: 744.09**
- **Purchasing power lost: 25.59%**
- **Real return (per year): 2.9126%**
- **Savings at that return, in today's money: 1,332.56**
- 검증 출처: Python decimal: 1000·1.03^10 = 1343.9164; 1000/1.03^10 = 744.0939; 1.06/1.03 − 1 = 2.912621 %

### Zero inflation

- Amount today: 1000
- Inflation rate (per year): 0%
- 년: 10
- Return on savings (per year): 6%
- **Future cost of the same purchase: 1,000.00**
- **Purchasing power lost: 0.00%**
- **Real return (per year): 6.0000%**
- **Savings at that return, in today's money: 1,790.85**
- 검증 출처: With π = 0 the real rate equals the nominal rate; 1000·1.06^10 = 1790.8477 (Python decimal)

### Deflation of 2% for 5 years

- Amount today: 100
- Inflation rate (per year): -2%
- 년: 5
- Return on savings (per year): 1%
- **Future cost of the same purchase: 90.39**
- **What the amount will buy, in today's money: 110.63**
- **Real return (per year): 3.0612%**
- 검증 출처: Python decimal: 100·0.98^5 = 90.3921; 100/0.98^5 = 110.6292; 1.01/0.98 − 1 = 3.0612 %

### 50,000 at 6.5% for 20 years

- Amount today: 50,000
- Inflation rate (per year): 6.5%
- 년: 20
- Return on savings (per year): 8%
- **Future cost of the same purchase: 176,182.25**
- **Total price rise: 252.36%**
- **Real return (per year): 1.4085%**
- 검증 출처: Python decimal: 50000·1.065^20 = 176182.2532; 1.08/1.065 − 1 = 1.40845 %

## 자주 묻는 질문

### How do you calculate the future cost of something with inflation?

Multiply today's price by (1 + inflation rate) raised to the number of years. At 3% a year, something costing 1,000 today costs 1,000 × 1.03^10 = 1,343.92 in 10 years, a total price rise of 34.39%. At 3.4% a year it would cost 1,397.03.

### How do you calculate the real rate of return after inflation?

Divide (1 + nominal return) by (1 + inflation) and subtract 1, the Fisher relation. Savings earning 6% while prices rise 3% have a real return of 1.06 ÷ 1.03 − 1 = 2.9126% a year. The shortcut 6% − 3% = 3% overstates it slightly, and the gap grows with higher rates.

### What is the current US inflation rate?

US consumer prices (CPI-U) rose 3.4% in the 12 months to August 2026, and 2.4% excluding food and energy, according to the Bureau of Labor Statistics. The Federal Reserve's target is 2% a year, measured by the PCE price index rather than the CPI; the Bank of England and the European Central Bank also target 2%.

### How long does it take inflation to halve the value of money?

ln 2 ÷ ln(1 + inflation rate) years. At 2% inflation cash loses half its purchasing power in 35.0 years, at 3% in 23.4 years and at 3.4% in 20.7 years. Even at a 2% target rate, 1,000 held as cash for 10 years loses 17.97% of what it can buy.

### “Inflation calculator (future cost and purchasing power)”의 정확도는 어느 정도인가요?

정확도는 입력값과 계산 방법의 가정에 따라 달라집니다. 십진 연산은 유효숫자 50자리를 사용하지만, 추정값·수치해석 방법·원본 데이터의 정밀도는 더 낮을 수 있습니다. 표시값을 반올림해도 이러한 한계는 사라지지 않습니다. 독립적인 출처의 풀이와 대조한 계산 예시: 4. 예를 들어 “1,000 at 3% inflation for 10 years, savings at 6%”은 Python decimal: 1000·1.03^10 = 1343.9164; 1000/1.03^10 = 744.0939; 1.06/1.03 − 1 = 2.912621 %와 대조해 확인합니다.

### 이 계산 방법의 출처는 무엇인가요?

U.S. Bureau of Labor Statistics — CPI inflation calculator; Fisher, I. — The Theory of Interest (1930), real vs nominal rates.

## 출처

- [U.S. Bureau of Labor Statistics — CPI inflation calculator](https://www.bls.gov/data/inflation_calculator.htm)
- Fisher, I. — The Theory of Interest (1930), real vs nominal rates

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