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Investing & Savings

Interest Calculator

Calculate compound growth from a starting balance, recurring contributions, rate, and time.

Best for: Project compound growth from a starting balance, recurring contributions, annual rate, and time horizon.

Your assumptions

Calculate your estimate

Your result

Interest estimate

Projected balance
$300,850.72
Total contributions
$130,000.00
Estimated growth
$170,850.72

Where the projected balance comes from

How to use this interest calculator

Use this interest calculator to project a balance built from principal, recurring deposits, and compound growth. It makes the contribution-versus-return split visible so a long-range estimate is not mistaken for guaranteed interest.

  1. 1

    Enter the starting balance

    Use the amount currently available to earn interest or investment returns.

  2. 2

    Add contributions and rate

    Enter a sustainable monthly deposit and a realistic annual return or yield.

  3. 3

    Compare time horizons

    Change the number of years to see how later compounding affects growth.

Worked planning example

Example: grow savings with monthly deposits

Set up

Start with $10,000, add $500 monthly, and use a moderate annual rate over 20 years.

Compare

Compare the same deposits at a lower rate and a shorter horizon.

Takeaway

Consistent contributions often drive early progress, while compounding becomes more influential later.

Separate guaranteed yield from assumed return

The appropriate rate depends on whether the money is in a deposit account, bond, or market investment.

  • Use an after-fee rate where possible.
  • Test a conservative return case.
  • Account for taxes and inflation separately.

Calculation methodology and assumptions

For this interest estimate, Silvia uses starting amount, monthly contribution, estimated annual return, time horizon. Calculate compound growth from a starting balance, recurring contributions, rate, and time. Results are estimates, not quotes, tax advice, or investment recommendations.

Frequently asked questions

Does this use compound interest?

Yes. The projection compounds the entered annual rate while adding recurring contributions.

Are monthly contributions made at the start or end of the month?

The formula uses a consistent monthly contribution convention. Actual timing can produce a small difference.

Is the projected interest guaranteed?

No. Only contractual deposit or security terms may be guaranteed; market returns can vary and may be negative.

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