2026-09-21 7 min read

Weekly Investment Calculator

Future value of fixed weekly contributions plus starting capital. Live calculator with worked steps, charts and year-by-year growth.

Calculator

Initial Investment Help

Money invested today before any contributions.

Contribution per Period Help

Amount added each contribution period.

Contribution Frequency

Expected Annual Return(%) Help

Nominal annual return before fees, taxes and inflation.

Time Horizon(years)

years

Annual Fee / Expense Ratio(%)

This contributions & timing calculator compounds at the nominal annual return with end-of-period contributions. Growth is rounded for display; maths runs at full precision.

Year-by-year growth

Year	Contributions	Growth	Balance
Year 1	$6,500.00	$532.92	$12,033
Year 2	$6,500.00	$990.06	$19,523
Year 3	$6,500.00	$1,476.92	$27,500
Year 4	$6,500.00	$1,995.42	$35,995
Year 5	$6,500.00	$2,547.62	$45,043
Year 6	$6,500.00	$3,135.72	$54,679
Year 7	$6,500.00	$3,762.04	$64,941
Year 8	$6,500.00	$4,429.07	$75,870
Year 9	$6,500.00	$5,139.46	$87,509
Year 10	$6,500.00	$5,896.02	$99,905

Results

Optimal

Projected Future Value

$99,905

Value after 10 years at 7.00%.

Total Amount Invested

$70,000

Growth From Returns

$29,905

Effective Annual Growth (CAGR)

34.92%

Contributions per Year

$6,500

Growth Multiple

1.43×

Time Horizon

10 years

Live results update as you type — currently showing projected future value of $99,905 over 10 years. Replace the defaults with your own plan for an exact comparison.

Visualizations

Growth Added Each Year

533Y1

990Y2

1,477Y3

1,995Y4

2,548Y5

3,136Y6

3,762Y7

4,429Y8

5,139Y9

5,896Y10

Where the Value Comes From

Initial5%

Contributions65%

Growth30%

Balance Over Time

Formula

The lump sum compounds for the full horizon while each contribution compounds for its remaining time; together they give the future value.

FV = PV(1+r)^t + PMT×(((1+i)^n−1)/i)

Variables

Symbol	Name	Unit	Description
PV	Present value	$	Amount invested today
FV	Future value	$	Projected value at the horizon
r	Annual return	%	Nominal annual return before fees/taxes
t	Time	years	Years invested
PMT	Contribution	$/period	Amount added each period

Explanation

This is what the plan is worth at the horizon if the return holds and contributions continue.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Grow the initial investment with compound interest.

FV = PV × (1 + r)^t

Initial:$5,000

Rate:7.00%

Years:10

Result: $9,836 from the lump sum

Step 2

Grow the contribution stream (52 per year) as an annuity.

FV = PMT × (((1 + i)^n − 1) / i)

Per-period contribution:$125

Periods per year:52

Result: $94,046 from contributions

Step 3

Add both parts and subtract what was invested to isolate growth.

Growth = FV − invested

Invested:$70,000

Result: $29,905 of compounding

Final Answer

$99,905

Worked Examples

See how the calculator works with different scenarios.

Scenario

The weekly investment calculator run on the values above, showing the full calculation path.

Inputs

Initial Investment:5000

Contribution per Period:125

Contribution Frequency:52

Expected Annual Return:7

Calculation

1. Grow the initial investment with compound interest. → $9,836 from the lump sum 2. Grow the contribution stream (52 per year) as an annuity. → $94,046 from contributions 3. Add both parts and subtract what was invested to isolate growth. → $29,905 of compounding

Result

Projected Future Value: $99,905

Interpretation

FV $99,905 from $70,000 invested (34.92% effective) over 10 years at 7.00% nominal less 0.50% fees.

Understanding Your Result

Your Result: Projected Future Value: $99,905

Typical range: A diversified portfolio at 7.00% roughly doubles every 10.2 years; contributions dominate early, compounding dominates after year 10–15.

What This Means

This is what the plan is worth at the horizon if the return holds and contributions continue.

Why It Matters

FV $99,905 from $70,000 invested (34.92% effective) over 10 years at 7.00% nominal less 0.50% fees.

Professional Interpretation

FV $99,905 from $70,000 invested (34.92% effective) over 10 years at 7.00% nominal less 0.50% fees.

How this is calculated

The lump sum compounds for the full horizon while each contribution compounds for its remaining time; together they give the future value.

What drives the result

Each period the balance grows by the return on what is already invested, then new contributions are added. Because growth applies to an ever-larger base, results accelerate over time: the last five years of a 30-year plan typically create more wealth than the first fifteen. Fees, taxes and inflation each act as a negative compounding rate against the same base.

Recommendations

•Automate contributions so compounding never pauses.
•Reinvest all distributions — uninvested cash breaks compounding.
•Re-run yearly with a conservative rate for planning.

Educational Content

Introduction

Investment growth is compounding: returns earned on principal and on prior returns. One equation — future value from a lump sum plus an annuity of contributions — prices every projection on this page, which is why rate, time and contributions move all results together.

Concept Explanation

Applications

▸Projecting retirement, college and house-deposit balances

▸Comparing lump-sum vs regular-contribution strategies

▸Stress-testing plans at lower returns

▸Measuring CAGR, ROI and profit on past investments

▸Adjusting nominal results for inflation, fees and taxes

Benefits

•Turns small regular contributions into large sums over decades
•Rewards starting early more than any other lever
•Gives a single math framework for goals, gaps and trade-offs
•Makes fee and tax drag visible in dollars, not basis points

Limitations

•Assumes a smooth constant return; real markets are volatile and sequenced
•Ignores taxes and fees unless the mode models them explicitly
•Single-point projections hide the distribution of outcomes

Best Practices

•Plan at 5–7% nominal for diversified portfolios; treat higher as upside
•Automate contributions and reinvest every distribution
•Re-run yearly and rebalance to the target allocation
•Evaluate spending goals in inflation-adjusted (real) terms

Common Misconceptions

Myth: Compound interest needs large sums to matter.

Truth: Small amounts compound dramatically over decades: $500/month at 7% exceeds $600,000 in 30 years, most of it growth.

Myth: The average return is what you earn each year.

Truth: Markets swing around the average. CAGR (geometric mean) is the honest multi-year number; arithmetic averages overstate wealth.

Myth: More frequent compounding transforms results.

Truth: Monthly vs annual compounding adds roughly half the rate in yield (6% → ~6.17%). Rate and time dominate; frequency is minor.

Practical Tips

•Use conservative inputs for planning and treat higher outcomes as upside.
•Re-run yearly; plans must survive reality.

Common Mistakes

Using one fixed return as a promise

Treat projections as scenarios. Test at 2 points lower before committing.

Ignoring fees, taxes and inflation

Each compounds against you. Check those views before deciding.

Assumptions

This calculator makes the following assumptions to provide estimates:

Constant smooth returns: Real returns vary year to year; the path affects timing but the long-run maths holds.

Limitations

Be aware of these limitations when using this calculator:

Limitation: Assumes a smooth constant return; real markets are volatile and sequenced

Limitation: Ignores taxes and fees unless the mode models them explicitly

Limitation: Single-point projections hide the distribution of outcomes

Frequently Asked Questions

Answers to common questions about this calculator.

How should I use this number?

This is what the plan is worth at the horizon if the return holds and contributions continue.

What would change it most?

Time first, contribution amount second, return third — compounding frequency and timing are minor by comparison.

Who uses the weekly investment calculator?

It is used by weekly savers and payday investors. It sits in the Contributions & Timing group of the Investing & Wealth section of Atlascalcs.

How accurate is the weekly investment calculator?

Every figure follows directly from the inputs using standard investment mathematics, so it is accurate to the quality of the values you enter. Real market returns vary year to year, so treat single-point projections as scenarios and test at lower returns before deciding.

How accurate is this calculator?

Figures follow directly from the inputs using standard investment mathematics, so accuracy equals input quality. Real returns vary year to year; treat results as scenarios, not promises.

Should I use nominal or real returns?

Use nominal for account balances and real (inflation-adjusted) for spending goals. A 7% nominal plan at 3% inflation only buys ~3.9% more each year.

Related Calculators

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Related Guides

Deepen your understanding with these educational resources.

Investing 101: compounding, allocation and costs

How growth, contributions and fees combine over decades.

Retirement planning with contribution math

Turn goals into per-period numbers and stay funded.

Risk-adjusted returns explained

Sharpe, Sortino, beta and drawdowns in plain language.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Compound interest: Interest earned on principal and on previously accumulated interest, producing exponential growth.
Future value (FV): Projected value of an investment or contribution stream at a future date under a stated return.
Dollar-cost averaging: Investing fixed amounts regularly, buying more shares when prices are low.
CAGR: Compound annual growth rate — the geometric mean yearly return turning start into end value.

Authoritative References

Trusted sources and standards referenced by this calculator.

SEC — Investor education and compound interest FINRA — Investing basics and fund costs IRS — Investment income, capital gains and retirement plans Federal Reserve — Interest rates and economic data (FRED) CFPB — Investing and retirement resources Bureau of Labor Statistics — Inflation (CPI)

Applicable Standards

CAGR as geometric mean for multi-year growth claimsFisher equation for real vs nominal returnsNPV/IRR discounting with end-of-period cashflowsMoney rounded for display only; all calculations run at full precision

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Page Information

Last Updated:

2026-09-21

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.