How this instrument works
Return on investment is the plainest return measure there is: take what a holding is worth now, subtract what it cost, and divide the difference by that original cost. The result is a percentage that says nothing about how fast the money moved, only how much came back relative to how much went in. A rental property flipped after eight months and a bond held for six years can both post the same ROI figure, and the number will not tell you which used your capital better — that question needs a time-aware measure alongside it.
Dividing by cost rather than subtracting alone is what makes the figure comparable across wildly different sizes of investment. A $500 gain means something different on a $1,000 stake than on a $100,000 one, and expressing it as a ratio strips out the scale so a $50 flea-market resale and a $50,000 renovation can sit on the same footing. Multiplying by 100 just moves the decimal so the answer reads as a percentage instead of a fraction — 0.50 becomes the more familiar 50 percent.
Two things this figure quietly leaves out matter. It assumes a single lump sum in and a single lump sum out, so it does not fit money added in stages — a portfolio topped up every month needs a money-weighted return instead. And it is silent on how the outcome was reached: brokerage commissions, closing costs, taxes on the gain, or the risk carried along the way all sit outside the two numbers you typed in, unless you have already folded them into cost or final value yourself.
- Enter Amount invested, $ — the actual cost you paid, before any later top-ups.
- Enter Final value, $ — what the holding is worth today, or what you sold it for.
- Read Return on investment, % — the gain as a share of what you originally put in.
- Read Net gain — the plain dollar difference, handy for comparing against costs quoted in dollars rather than percent.
- Swap in a smaller final value to see the same arithmetic report a loss as a negative percentage.
Worked example — a $1,000 stake becomes $1,500
Amount invested, $ 1,000. Final value, $ 1,500. Net gain is the plain subtraction, 1,500 minus 1,000, which comes to $500. Dividing that $500 by the original $1,000 gives 0.50, and multiplying by 100 turns it into the figure the readout shows: Return on investment, % 50.
The same $500 gain would read as a smaller percentage against a bigger stake and a larger one against a smaller stake, which is exactly why the ratio, not the raw dollar figure, is what gets compared across different deals. Change Final value, $ to 500 instead of 1,500 and the sheet reports a gain of −$500 and an ROI of −50 percent — the identical arithmetic, run on a loss.
Questions
Does ROI account for how long I held the investment?
No, and that is deliberate — this figure reads two endpoints only, cost and final value, with no clock attached. An eight-month flip and an eight-year hold that both double your money post an identical 100 percent ROI. To compare speed of return across different holding periods, an annualised measure such as a compound annual growth rate is the right tool, not this one.
Is ROI the same thing as profit margin?
No — they divide by different numbers. Margin measures profit against revenue (what a sale brought in), while ROI measures gain against cost (what was put in to begin with). A product selling for $150 that cost $100 to make has a 33 percent margin but a 50 percent ROI on that $100, because the two ratios are answering different questions.
Why can't a 50 percent loss be undone by a 50 percent gain?
Because the base each percentage is measured against changes. Losing 50 percent of $1,000 leaves $500; a 50 percent gain on that smaller $500 only returns $250, landing at $750 total, still short of the start. Reaching back to $1,000 from $500 needs a 100 percent gain — the asymmetry grows sharper the deeper the loss.
Should fees and taxes be folded into cost and final value?
Only if you want a figure that reflects what actually landed in your pocket. This sheet takes both numbers exactly as entered — it does not know about a brokerage commission or a closing cost unless you have added it to Amount invested, $, and it does not know about tax owed on the gain unless you have already subtracted it from Final value, $.
Why does a negative Final value, $ break the calculation?
It does not break, but zero or negative Amount invested, $ does — dividing by zero has no answer, and the checks on this sheet block it outright. Final value, $ itself is free to run below cost; that is simply what a loss looks like, and the sheet reports the resulting negative gain and negative percentage without complaint.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.