Purchasing Power Halving Calculator
Model erosion under assumed inflation.
Purchasing Power Halving Calculator: Scenario Inputs
Annual percentage rate or benchmark index change.
Inflation & Purchasing Power Analysis
Over 3 years at 3.5% inflation, a $75,000 salary requires $83,154 to retain equal purchasing power. Without matching raises, your real compensation experiences an effective reduction of $7,355 (-9.81%).
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How Purchasing Power Halving Calculator Works?
The Purchasing Power Halving Calculator works by solving for the number of years at which prices double.
Enter an inflation rate
Type the assumed annual rate, such as 3.5%.
Enter an amount
Type a salary or savings balance to see its half-value in dollars.
Solve for time
The calculator divides the natural log of 2 by the natural log of 1 + rate.
Compare with the rule of 70
The output shows the exact years next to the quick estimate of 70 ÷ rate.
Purchasing Power Halving Calculator Formula
The Purchasing Power Halving formula divides the natural logarithm of 2 by the natural logarithm of one plus the inflation rate.
Years = ln(2) ÷ ln(1 + i)
Years ≈ 70 ÷ (i × 100)
Variables
- i
- Annual inflation rate as a decimal
- ln
- Natural logarithm
Worked example
At 4% inflation, purchasing power halves in 17.67 years. The rule of 70 gives 17.5 years. A fixed $80,000 salary buys what $40,000 buys today after that time.
Purchasing Power Halving Calculator Conversion Table
This table lists halving times for 6 inflation rates, with the rule-of-70 estimate and the halving time in months.
| Inflation rate | Exact years to halve | Rule of 70 | Months to halve |
|---|---|---|---|
| 2% | 35.00 | 35.0 | 420 |
| 3% | 23.45 | 23.3 | 281 |
| 4% | 17.67 | 17.5 | 212 |
| 5% | 14.21 | 14.0 | 170 |
| 7% | 10.24 | 10.0 | 123 |
| 10% | 7.27 | 7.0 | 87 |
What is Purchasing Power Halving Calculator?
The Purchasing Power Halving Calculator is a tool that calculates how many years it takes for a fixed salary or sum to lose half of its purchasing power at an assumed inflation rate. The halving time is the inflation version of a doubling time.
At 3% inflation a fixed salary halves in real value in 23.4 years. At 7% the same loss takes 10.2 years.
What are the uses of Purchasing Power Halving Calculator?
There are 4 main uses of the Purchasing Power Halving Calculator.
Show long-run risk
Explain how a fixed salary loses half its value within one career.
Plan retirement income
Show retirees with fixed pensions when real income falls by 50%.
Compare inflation regimes
Contrast halving times under 2%, 5% and 10% inflation.
Teach compounding
Give students a quick rule for inflation's long-term effect.
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