Calculate inflation between two dates
Enter a Starting amount ($) greater than 0, a valid Start date, and a valid End date. The end date must be after the start date. The start date can be in the past or future.
- Enter the starting amount and dates.
- Choose Single annual rate or Year-by-year rate series.
- Enter the rate or rates. Use a negative percentage for deflation. In series mode, click Build year fields from dates first, then complete every generated field.
- Optionally enter Ending nominal amount ($) to compare nominal and real change.
- Click Calculate. Use Copy result or Download result (.txt) to keep the output, or click Reset to clear the form.
Choose a rate method
Use Single annual rate to apply one user-entered annual percentage across the whole period. Use Year-by-year rate series when you want a separate percentage for each calendar year touched by the dates.
In series mode, enter valid dates and click Build year fields from dates. Complete every generated field. If you change either date afterward, click Build year fields from dates again because the fields are not rebuilt automatically.
Read the results
After calculation, the result shows Cumulative inflation, Equivalent value at end date, and Years elapsed. Money values use USD formatting. The equivalent value is the starting amount adjusted by the rates you entered, not an official CPI-based estimate.
If you entered an Ending nominal amount ($), the result also shows Nominal change and Real change (inflation-adjusted).
When Year-by-year rate series is selected, the year-by-year breakdown appears after calculation. It lists each rate, the portion of the year in the date range, and the resulting factor.
How the calculation treats rates and time
Rates are entered as percentages and converted with rate / 100. In series mode, each calendar year uses:
Year factor = (1 + rate_y / 100)^fraction_y
The year factors are multiplied to get the cumulative factor. Single-rate mode uses:
Cumulative factor = (1 + rate / 100)^years
For single-rate elapsed time, years = days between dates / 365.25. Series mode uses the implementation's calendar-year fraction for each year. The displayed values then use Cumulative inflation % = (Cumulative factor - 1) × 100 and Equivalent value = Starting amount × Cumulative factor.
With an ending nominal amount, the calculator uses Nominal change % = (Nominal end - Starting amount) / Starting amount × 100 and Real change % = [(1 + Nominal change % / 100) / Cumulative factor - 1] × 100.
Validation and limitations
- Starting amount ($) must be greater than 0. If supplied, Ending nominal amount ($) must be 0 or greater.
- Both dates are required and must be valid, and the end date must be after the start date.
- Single annual rate requires an entry in Annual inflation rate (%). Year-by-year rate series requires you to click Build year fields from dates and complete every generated rate field.
- You supply every rate. The calculator does not fetch live CPI, official inflation indexes, or inflation rates.
- It does not automatically model category or regional variation, perform currency conversion, or provide financial advice.
- Rates at or below
-100%are rejected because the calculation uses a fractional power; enter a rate above-100%. - The calculation runs in your browser. This page also loads site-wide analytics.
Frequently asked questions
Does this calculator use official CPI or government inflation data?
No. It does not fetch live CPI, official inflation indexes, or inflation rates. You enter either one annual rate or a year-by-year rate series, and the calculator compounds those numbers. It does not look up or guarantee official inflation figures.
How is cumulative inflation calculated?
Each year uses (1 + rate / 100)^fraction, where the rate is your percentage entry and the fraction is the portion of that calendar year in the date range. The factors are multiplied, then cumulative inflation is (factor - 1) × 100.
What is the difference between the single-rate and year-by-year modes?
Single annual rate applies one constant annual percentage across the period. Year-by-year rate series lets you enter a different percentage for each calendar year the period touches.
What is real vs. nominal change?
Nominal change is the percentage change between the starting amount and the optional ending nominal amount. Real change adjusts that change by the cumulative inflation factor. These values appear only when you enter an ending nominal amount.
Is this investment or financial advice?
No. This is a mathematical calculation based on the amount, dates, and rates you supply. It does not recommend investments or replace professional financial advice.