How To Calculate Average Monthly Return In Excel

Calculate your investment’s average monthly return with this precise Excel-style calculator

Comprehensive Guide: How to Calculate Average Monthly Return in Excel

Calculating average monthly returns is essential for investors to evaluate performance, compare investments, and make data-driven decisions. This guide will walk you through multiple methods to calculate monthly returns in Excel, including formulas, functions, and advanced techniques.

Understanding Monthly Returns

Monthly return measures the percentage change in an investment’s value over a one-month period. It’s calculated as:

Monthly Return = (Ending Value – Beginning Value) / Beginning Value

For multi-period calculations, we use geometric averaging to account for compounding effects.

Basic Monthly Return Calculation in Excel

1. Simple Percentage Change:
   • Enter beginning value in cell A1 (e.g., $10,000)
   • Enter ending value in cell B1 (e.g., $10,500)
   • Use formula: = (B1-A1)/A1
   • Format as percentage (Ctrl+Shift+%)
2. For Multiple Months:
   • Create a column with monthly values
   • Use: = (B2-B1)/B1 and drag down
   • Calculate average: = AVERAGE(C2:C13)

Geometric vs. Arithmetic Mean

For investment returns, geometric mean is more accurate because it accounts for compounding:

= GEOMEAN(1+returns_range)-1

Where returns_range contains your monthly percentage returns (as decimals).

XIRR Function for Irregular Cash Flows

For investments with contributions/withdrawals:

1. List all cash flows with dates
2. Use: = XIRR(values_range, dates_range)
3. Convert to monthly: = (1+XIRR_result)^(1/12)-1

Advanced Excel Techniques

Method	Formula	Best For	Accuracy
Simple Average	=AVERAGE(returns)	Quick estimates	Low
Geometric Mean	=GEOMEAN(1+returns)-1	Multi-period returns	High
Logarithmic Returns	=EXP(AVERAGE(LN(1+returns)))-1	Volatile investments	Very High
XIRR Method	=XIRR(values, dates)	Irregular cash flows	Highest

Common Mistakes to Avoid

• Using arithmetic mean: Overestimates returns by ignoring compounding
• Ignoring time weighting: Equal-weighting months with different lengths
• Miscounting periods: Using 12 months ≠ 1 year for compounding calculations
• Data entry errors: Always verify your beginning/ending values
• Forgetting contributions: Additional cash flows must be accounted for

Real-World Example: S&P 500 Returns

Let’s analyze actual S&P 500 monthly returns from 2010-2020:

Year	Arithmetic Mean	Geometric Mean	Actual Return
2010	1.82%	1.78%	15.06%
2011	0.51%	0.49%	2.11%
2012	1.36%	1.34%	16.00%
2013	2.15%	2.12%	32.39%
2014	1.30%	1.28%	13.69%
10-Year Avg	1.43%	1.40%	13.90%

Notice how the geometric mean (1.40%) more accurately reflects the actual 10-year return (13.90%) when compounded, compared to the arithmetic mean (1.43%) which would overestimate the final value.

Excel Automation with VBA

For frequent calculations, create a custom function:

1. Press Alt+F11 to open VBA editor
2. Insert > Module
3. Paste this code:

   Function GeoMeanMonthly(Rng As Range) As Double
       Dim i As Long
       Dim Product As Double
       Product = 1
       For i = 1 To Rng.Count
           Product = Product * (1 + Rng.Cells(i, 1).Value)
       Next i
       GeoMeanMonthly = (Product ^ (1 / Rng.Count)) - 1
   End Function
                   

4. Use in Excel: =GeoMeanMonthly(A1:A12)

Visualizing Returns with Excel Charts

To create a professional return chart:

1. Select your date and return data
2. Insert > Line Chart
3. Add a secondary axis for cumulative returns
4. Format data series:
   • Monthly returns: Blue line with markers
   • Cumulative: Green area chart
   • Average line: Red dashed
5. Add data labels for key points

External Resources

For additional learning, consult these authoritative sources:

• U.S. Securities and Exchange Commission – Compound Interest Guide
• Corporate Finance Institute – Geometric Mean in Finance
• NYU Stern – Historical Returns Data

Frequently Asked Questions

Q: Why use geometric mean instead of arithmetic?

A: Geometric mean accounts for compounding effects. If you lose 50% one month and gain 50% the next, arithmetic average is 0%, but geometric shows -13.4% actual return.

Q: How to annualize monthly returns?

A: Use = (1+monthly_return)^12-1. For our calculator’s 1.40% monthly, that’s 18.25% annualized.

Q: Can I calculate returns with dividends?

A: Yes! Include dividends in your ending value calculation. For monthly returns, add dividends to the month they’re received.

Final Recommendations

1. Always use geometric mean for multi-period returns
2. Account for all cash flows (dividends, contributions)
3. Verify your time periods (actual months vs. 30-day periods)
4. Consider using XIRR for irregular cash flows
5. Visualize your returns to spot patterns
6. Compare against benchmarks (S&P 500, sector averages)

By mastering these Excel techniques, you’ll gain deeper insights into your investment performance and make more informed financial decisions. The calculator above provides a quick way to verify your Excel calculations and visualize your returns.