Investment calculator

Project how a starting amount and regular monthly investing could grow over time, or measure the return on an investment you’ve already made, including its annualized return.

By OpenBookMoney Editors · Free, no sign-up · Updated Oct 15, 2026

ROI & investment growth calculator

Project how an investment could grow with regular contributions — or measure the return on one you already made.

Projected value after 15 years $120,922 About $83,492 in today’s money at 2.5% inflation
Total contributed $64,000
Investment growth $56,922
Return on contributions 88.9%
Doubling time (Rule of 72) 10.3 years

Adding $100 more per month could grow your balance by an extra $31,110 over 15 years.

Projected growth Year 15 · $120,922 ($64,000 contributed)
Total contributed Investment growth

Year-by-year projection

Year Contributed Growth Balance Today’s money
1 $13,600 $814 $14,414 $14,063
2 $17,200 $1,937 $19,137 $18,215
3 $20,800 $3,391 $24,191 $22,464
4 $24,400 $5,198 $29,598 $26,815
5 $28,000 $7,384 $35,384 $31,275
6 $31,600 $9,975 $41,575 $35,850
7 $35,200 $13,000 $48,200 $40,549
8 $38,800 $16,488 $55,288 $45,377
9 $42,400 $20,472 $62,872 $50,343
10 $46,000 $24,987 $70,987 $55,455
11 $49,600 $30,070 $79,670 $60,720
12 $53,200 $35,761 $88,961 $66,148
13 $56,800 $42,103 $98,903 $71,746
14 $60,400 $49,140 $109,540 $77,524
15 $64,000 $56,922 $120,922 $83,492

How it’s calculated

Each month the balance grows by the monthly equivalent of your annual return, i = (1 + r)^(1/12) − 1, and then your contribution is added. Contributions rise once a year by the step-up rate. Value in today’s money = Balance ÷ (1 + inflation)^years.

Projections assume a constant return; real investments rise and fall, and past performance does not guarantee future results. Taxes and fees are not included in the projection. Estimates only — not financial advice.

Two ways to use the investment calculator

  • Projection: enter your initial investment, monthly contribution, expected annual return and the number of years. You can raise contributions each year and see results in today’s money after inflation.
  • Actual return (ROI): enter what you invested, the current or sale value, any income received such as dividends, the fees you paid and how long you held it.

The year-by-year projection shows how much of your balance comes from contributions and how much from growth.

How the calculations work

Projection: each month the balance grows by the monthly equivalent of the annual return, i = (1 + r)1/12 − 1, and then your contribution is added.
ROI = (value + income − fees − amount invested) ÷ amount invested
Annualized return = (1 + ROI)1 ÷ years − 1

Example: investing $300 a month

Start with a hypothetical $10,000, add $300 a month and assume a 7% average annual return for 15 years. You would contribute $64,000 in total and could end with about $120,900, so roughly $56,900 would come from growth. Real returns vary from year to year and can be negative.

For a past investment: if $5,000 grew to $7,800 over four years and paid $240 in dividends, with $20 in fees, the total return is 60.4%, or about 12.5% a year.

What return should I expect?

No one knows future returns. Diversified stock funds have historically grown faster than cash or bonds over long periods, but with large swings along the way. Try a cautious, a middle and an optimistic rate to see a range instead of a single number, and remember that taxes and fees reduce what you keep.

Ways to grow your investments

  • Invest regularly. Investing a fixed amount each month, known as dollar-cost averaging, builds the habit and smooths out timing.
  • Keep costs low. A 1% fee can take a large bite out of decades of growth; see it with our fund fee calculator.
  • Diversify. Broad index funds and ETFs spread risk across many companies.
  • Use tax-advantaged accounts such as a 401(k) or IRA when you can. Our 401(k) calculator includes employer matching.
  • Give it time. The longer your money stays invested, the more compounding can work.

Frequently asked questions

What is ROI?

Return on investment (ROI) is your total gain, including income and after fees, divided by what you invested. It tells you how much you earned per dollar invested, but not how long it took.

Why look at the annualized return?

It turns a total return into a yearly rate, so you can compare investments held for different lengths of time.

Does the projection include taxes and fees?

No. The projection assumes a constant return before taxes and fees. Enter fees in the ROI mode, or lower the expected return to allow for them.

How is this different from the compound interest calculator?

The compound interest calculator models a single deposit at a fixed rate. This calculator adds monthly contributions, annual increases and inflation.

Projections assume a constant return; real investments rise and fall, and past performance does not guarantee future results. Not financial advice.