Inflation Calculator

Inflation calculator 2026 online. Convert money value between dates

This tool helps you check how much a given amount from the past corresponds to today and how the purchasing power of money has changed over time. You enter the amount, select the starting and ending month and year, and the calculator calculates the adjusted value, the total inflation factor, the change in PLN and the number of months. You can use the built-in CPI for Poland, use a fixed annual rate or paste your own CSV file with indexes.

What the calculator calculates and who it is intended for

The tool answers three practical questions. What is the current equivalent of the indicated amount from the past? What is the total change resulting from inflation in PLN. What was the cumulative inflation rate for the selected range. The calculator is used by people comparing costs over time, business owners verifying budgets, buyers and sellers analyzing the real value of transactions, as well as anyone who wants to understand the impact of inflation on savings and expenses.

Input. What do you enter

• Initial amountin PLN. Enter the gross or net amount according to your analysis.
• Start datemonth and year. It means the moment from which the amount comes.
• End datemonth and year. This is the moment you count to. The end date must be no earlier than the start date.
• Data source. Choices:
  • Built-in CPIPoland, monthly indices. A quick comparison option.
  • Annual inflation rateas a percentage. A fixed rate with monthly compounding gives you a smooth path between months.
  • Custom CSVwith monthly indexes in the formatYYYY-MM, index. Useful when working with other sources or countries.

After the conversion, you will see four values: the adjusted amount, the inflation factor, the real change and the number of months between the dates.

Step-by-step instructions

1. Enter the starting amount.
2. Set the start and end month and year.
3. Select a data source. For annual rate, enter percentage. If you are using your own CSV, paste lines in the formatYYYY-MM, index. The index can have any base, the important thing is the ratio of values ​​between dates.
4. ClickCalculate. The result will appear below the form.
5. If you want to start over, clickClear.

How to read the result

• The adjusted valueis the amount that represents the same purchasing power today as before.
• The cumulative inflation factorshows how many times the price level has changed over a given period.
• The real changeis the difference between the adjusted value and the initial amount. Positive means price increases.
• The number of monthshelps you understand the comparison horizon. The longer the period, the greater the cumulative effect.

Calculation examples. Built-in CPI for Poland

The table below illustrates approximate conversions of the amount of PLN 1,000 for September 2025. The values ​​are based on the built-in monthly CPI set. They are illustrative in nature and are used to quickly assess purchasing power over time.

Interpretation example. PLN 1,000 in January 2015 corresponds to approximately PLN 1,880 in September 2025. This means that the overall price level has increased by approximately 88 percent during this period. For shorter sections, the increase is smaller, which can be seen at the start in 2024.

Examples. Annual inflation rate

This option is convenient when you want to simulate inflation that is constant over time. You set the percentage per year, the calculator spreads it evenly between months and calculates the cumulative effect for your range.

In practice, the annual rate gives a simple, consistent result and works well with planning assumptions. If you want to reflect real monthly fluctuations, use CPI or your own CSV.

Custom CSV. When to

If you are working on a specific data source or another country, paste in your own set of monthly indexes. Each line should beYYYY-MM, index. The index is a positive number, for example 100.0, 112.7, 135.3. The base can be any month. What matters is the ratio of the value for the end date to the start date. This will allow the calculator to calculate the amount based on your source.

• Make sure the range includes start and end months.
• Use a dot as a decimal separator when copying from a spreadsheet with international settings. The tool also accepts a comma.
• Remove blank lines and table headings before pasting.

Most common uses

• Comparison of renovation valuation from several years ago with the current budget.
• Purchasing power analysis of savings from the selected month.
• Valoration of amounts in reports and presentations to make comparisons more realistic.
• Simple simulation of the impact of inflation on subscriptions and recurring fees.

Common mistakes and how to avoid them

• Inverted dates. If you select an end date earlier than the start date, the result will not be counted. Organize the scope.
• Mixing Data Sources. Compare results within one source. Changing the index methodology changes the result.
• Month missing in CSV. Make sure your file contains the exact months you are comparing.
• Confusing gross and net values ​​. Inflation is about price levels. Taxes and promotions are separate factors.

Practice Tips

• Use the built-in CPI for ongoing comparisons. For projects and contracts, consider a fixed annual rate as an assumption.
• When presenting results, include a date range and source so that your audience understands the context.
• For long horizons, it is worth showing both the adjusted amount and the total ratio. This makes it easier to understand the scale of the change.
• In CSV, keep the uniform month formatYYYY-MM. This will help you avoid parsing errors.

FAQ

Does the built-in CPI cover the entire period of

The built-in data is monthly and covers the most recent years. This is an overview set for quick analyses. If you need a different period or country, please use your own CSV.

Is the constant annual rate accurate

This is an approximation. It gives a smooth course without seasonality. Good for plans and simulations. It is better to use real indexes to reconstruct the past.

What currency does the calculator support

You enter the amounts in Polish zloty. If you count other currencies, treat the result as an index adjustment and multiply it by the exchange rate separately.

What does positive and negative real change mean

Positive means that prices have increased over the period. Negative means a decline in the overall price level. In recent years, we have mostly observed increases.

Safety and responsible use

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