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Monthly Return Calculator

The Monthly Return Calculator measures how much an investment gained or lost during a single month, expressed as both a dollar change and a percentage of the starting value. It is useful for investors reviewing brokerage statements, comparing monthly performance across accounts, or tracking a portfolio that receives deposits and withdrawals.

The basic result separates investment performance from account size. A positive percentage indicates growth, while a negative percentage indicates a loss. When cash flows occur during the month, the estimate should be interpreted carefully because deposits and withdrawals can distort a simple beginning-to-ending comparison.

Calculator inputs

$
$
$
Result
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Monthly return
Investment change—
Return rate—
Annualized equivalent—

1. Enter the starting value
Provide the investment or portfolio value at the beginning of the month.

2. Enter the ending value
Use the value at the end of the same month, after market movement and any income credited.

3. Add net cash flow if applicable
Enter deposits as positive amounts and withdrawals as negative amounts so the calculation can isolate the approximate investment change.

4. Review the monthly result
Compare the dollar return and percentage return, then use the same method consistently across months.

Formula

Net investment change = Ending value - Starting value - Net cash flowMonthly return (%) = (Net investment change / Starting value) × 100

Where

  • Starting value = account value at the beginning of the month
  • Ending value = account value at the end of the month
  • Net cash flow = deposits minus withdrawals during the month
  • Net investment change = estimated gain or loss attributable to performance

Assumptions

This is a simple monthly return model. It does not adjust for the exact timing of cash flows. For portfolios with large or frequent deposits and withdrawals, a time-weighted or money-weighted return may be more appropriate.

What the result means

Monthly return based on the values entered.

Results are estimates and may differ from payroll, tax, legal, investment, or accounting systems.

Given

• Starting value: $25,000

• Ending value: $26,150

• Net deposit during the month: $500

Calculation

Net investment change = $26,150 - $25,000 - $500 = $650

Monthly return = ($650 / $25,000) × 100 = 2.60%

Result

• Dollar return: $650

• Monthly return: 2.60%

Interpretation

After removing the $500 deposit, the portfolio gained an estimated $650 from investment performance during the month.

Should dividends be included in the ending value?

Yes. Include dividends and interest that were credited to the account, whether paid in cash or reinvested, unless you are intentionally measuring price return only.

How should I enter a withdrawal?

Treat a withdrawal as a negative cash flow. For example, a $300 withdrawal would be entered as -$300 if the field uses signed values.

Can I annualize the monthly return?

You can compound it using (1 + monthly return)^12 - 1, but a single month is rarely representative of a full year. Annualized figures should be labeled as projections, not actual annual performance.

Why can a deposit make the simple return look too high?

An ending balance includes both investment gains and added cash. Subtracting net cash flow prevents the deposit itself from being counted as return.

How is this different from an Investment Return Calculator?

This tool focuses on one monthly period. A broader investment return calculator may cover longer holding periods, multiple cash flows, or total return over several years.