Long-Term Purchasing Power: What It Means and How It Works
Saving 10,000 today doesn’t mean being able to buy the same amount with that 10,000 in twenty years. The number in the account may stay the same or even grow, but what that money can buy changes over time. That change is what is known as purchasing power, and understanding it over the long term is key to any savings or retirement planning.
What long-term purchasing power means
Purchasing power is the amount of goods and services that can be bought with a given amount of money. When talking about long-term purchasing power, it refers to how that buying capacity evolves over periods of several years or decades, usually in the context of savings, retirement, or any financial goal far off in time.
The central idea is simple: money itself doesn’t have a fixed value, it has value in relation to what it can be exchanged for. If prices rise and the amount of money stays the same, that money buys less than before. That gradual loss accumulates year after year and becomes very relevant when thinking about horizons of 15, 20, or 30 years.
How inflation affects saved money
Inflation is the widespread and sustained increase in the prices of goods and services in an economy. When inflation is 3% per year, a product that costs 100 monetary units today will cost approximately 103 the following year. If saved money doesn’t grow at an equal or higher rate, each year it allows buying a little less.
This effect isn’t noticeable from one year to the next, but it accumulates. The key is understanding the difference between two concepts:
- Nominal value: the exact figure that appears in the account, without adjusting for inflation.
- Real value: what that figure actually allows to be bought once the effect of accumulated inflation is subtracted.
To go deeper into each of these terms separately, there are specific articles about what nominal value means and how it’s calculated and about what real value means and how it’s calculated.
How cumulative inflation is calculated
Cumulative inflation is not calculated by multiplying the annual percentage by the number of years, because the effect is compound: each year inflation acts on prices already raised by the previous year’s inflation. The general formula for several periods is:
Cumulative inflation = (1 + i)^n − 1, where “i” is the annual inflation rate expressed as a decimal and “n” is the number of years.
With inflation of 3% per year over 20 years, the calculation would be (1 + 0.03)^20 − 1, which gives approximately 0.806, that is, 80.6% cumulative inflation. This means that after 20 years, 180.6 monetary units would be needed to buy what costs 100 today.
Example of loss of purchasing power
Suppose a person keeps 20,000 monetary units under the mattress, without generating any kind of return. With average inflation of 2.5% per year, after 25 years the real purchasing power of that money is calculated by dividing the nominal value by the cumulative inflation factor:
- Cumulative inflation factor: (1 + 0.025)^25 ≈ 1.854
- Equivalent real value: 20,000 / 1.854 ≈ 10,788 monetary units
The number in the account is still 20,000, but its buying capacity has dropped to a little less than half. This numerical example illustrates why keeping money without any kind of return for decades implies a silent but constant loss of value.
Why the time horizon amplifies the effect
The effect of inflation is exponential, not linear. In short periods, of one or two years, the loss of purchasing power may seem insignificant. But when extended to 20, 30, or 40 years, the result changes noticeably, because each year inflation is applied on a base of prices already inflated by previous years.
This is especially relevant in retirement planning, where money saved today may need to remain useful decades from now. The longer the horizon, the greater the importance of considering how purchasing power evolves, and not just the accumulated nominal figure.
Purchasing power and future savings
When designing savings meant for the future, the relevant question is not just “how much money will I have”, but “how much will I be able to buy with that money when I need it”. That distinction completely changes how long-term savings goals are understood.
For example, if the goal is to accumulate an amount that today would cover a certain level of monthly spending, that same level of spending, 20 or 30 years from now, will require a much higher nominal figure due to the cumulative inflation over that period. Ignoring this adjustment can lead to seriously underestimating how much needs to be saved.
How to estimate the future purchasing power of a savings goal
To estimate how much nominal money will be needed in the future to maintain a given purchasing power, the inverse formula to cumulative inflation can be applied:
Future amount needed = Desired current amount × (1 + i)^n
If today it’s considered that 1,500 monetary units per month cover an adequate spending level, and inflation of 2% per year is projected over 30 years, the calculation would be 1,500 × (1.02)^30 ≈ 1,500 × 1.811 ≈ 2,717 monetary units per month needed in 30 years to maintain the same current purchasing power.
This type of projection can be complex to calculate by hand when periodic contributions, returns, and different time horizons are combined. To simplify these calculations, there is a free savings projection calculator that allows entering variables such as initial capital, contributions, expected return, and number of years, obtaining an estimate of both the nominal value and the inflation-adjusted value.
Purchasing power in retirement planning
Retirement is one of the contexts where long-term purchasing power carries the most weight, because it combines two factors: a long time horizon until the money is available, and another later period during which that money must remain sufficient. Every year that passes, both before and during retirement, inflation keeps eroding the real value of the capital if it doesn’t generate some kind of return.
For this reason, any savings structure designed for retirement usually takes this effect into account from the initial design. It can be useful to review how a long-term savings plan is organized and structured to understand how these elements combine in practice.
Common mistakes when thinking about purchasing power
When planning savings, certain mistakes related to purchasing power are common:
- Setting savings goals in nominal terms without adjusting for future inflation.
- Comparing salaries or savings from different decades without accounting for the cumulative inflation between those periods.
- Assuming that keeping money without a return is equivalent to “not losing anything”, when in reality purchasing power is lost constantly.
- Not periodically reviewing savings projections to update inflation assumptions.
Avoiding these mistakes doesn’t require complicated calculations, just incorporating the inflation adjustment as a routine step within any financial projection related to future savings.
Frequently asked questions
What is long-term purchasing power?
It is the buying capacity that an amount of money has over several years or decades, considering how inflation progressively reduces what that money can acquire over time.
How does inflation affect saved money?
If prices rise every year and saved money doesn’t generate a return equal to or higher than that rise, the nominal amount stays the same but allows buying fewer and fewer goods and services, since its real value decreases cumulatively.
How is the loss of purchasing power calculated in a specific example?
The nominal value of the money is divided by the cumulative inflation factor, calculated as (1 + inflation rate) raised to the number of years. For example, with 20,000 monetary units and inflation of 2.5% per year over 25 years, the equivalent real value would be approximately 10,788 monetary units.
Why does purchasing power matter more the longer the term?
Because the effect of inflation is compound, not linear: each year it acts on prices that already rose the previous year. In short periods the effect is small, but over horizons of 20, 30, or 40 years, like those handled in savings or retirement planning, the difference between nominal value and real value becomes very significant.
Can you estimate how much money will be needed in the future to maintain the same current purchasing power?
Yes, by multiplying the desired current amount by the projected cumulative inflation factor for the years remaining until the moment that money will be needed. This type of calculation can be done more thoroughly with projection tools that also incorporate periodic contributions and expected returns.