Investment Growth Over Time Calculator

Investment growth calculator for compound interest, contributions, and time

This investment growth over time calculator estimates how your balance could change as you keep money invested and add regular contributions. It combines three simple drivers, an initial deposit, a repeating contribution amount, and compound growth. The output is not a promise of returns. It is a planning view that helps you understand how time and consistency can change outcomes.

To use it, enter your starting amount and a regular contribution. Pick an expected annual return and the number of years you plan to invest. Then choose how often you want returns to compound (monthly, quarterly, annually, and so on) and whether your contribution happens at the beginning or end of each period. The calculator will estimate a final balance, your total contributions, and the interest or growth earned on top of what you put in.

If you also enter an inflation rate, the calculator estimates a “today’s money” version of the final balance. This can be useful because a large future number can look impressive while still buying less in the future. Inflation adjustment is optional because inflation is uncertain and varies by country and time period. Use it as a rough sensitivity check, not as an exact forecast.

The yearly breakdown table is designed for reality checks. It shows how the balance may evolve at the end of each year. Early on, most of the balance is contributions. Later, growth starts to dominate. This is the core reason long horizons matter, the compounding effect needs time to become meaningful.

When comparing scenarios, change one input at a time. For example, keep the return rate the same and test different contribution amounts. Then keep contributions fixed and test different time horizons. This helps you see what is actually driving the difference rather than changing everything and guessing.

Assumptions and how to use this calculator

• Returns are assumed to be a steady average rate, compounding at the frequency you select. Real markets are volatile and will not follow a smooth path.
• Regular contributions are assumed to occur once per compounding period (not multiple times inside the period). If you select monthly compounding, treat the contribution as monthly.
• Taxes, fees, transaction costs, and account rules are not included. In real life, these can materially reduce net returns.
• If you choose “beginning of each period,” contributions are assumed to start earning returns immediately for that period. If you choose “end,” they start earning from the next period.
• The inflation adjustment uses a constant annual inflation rate over the full horizon. This is only an approximation of purchasing power.

Common questions

What does “expected annual return” mean?

It is an assumed average yearly growth rate before fees and taxes. For planning, people often use a conservative estimate rather than a best case. If you are unsure, test a low, medium, and high scenario to see how sensitive your results are to the rate.

What is the difference between compounding frequency and contribution timing?

Compounding frequency controls how often growth is applied to the current balance. Contribution timing controls whether you add money at the start or end of each compounding period. Beginning-of-period contributions generally produce a higher final balance because each contribution has more time to grow.

Why is the interest earned number sometimes larger than total contributions?

Over long horizons, growth can exceed what you personally contributed because returns start generating returns. This is the compounding effect. It tends to be slow early on and more dramatic later, which is why the time horizon is a major driver.

What if my return rate is 0%?

If the return rate is 0%, the model becomes simple arithmetic. Your final balance is your initial amount plus your contribution multiplied by the number of periods. The calculator handles this case explicitly so you still get a correct result.

How should I use the inflation adjusted value?

The inflation adjusted result estimates what your future balance might be “worth” in today’s purchasing power, given the inflation rate you entered. It is useful for comparing goals across time, but it is not precise. If you want to be conservative, use a slightly higher inflation rate and a slightly lower expected return.