Backtest final value — four truths hidden in one number

Run a backtest and the result screen shows a big number in one line. Something like "$180,000 after 5 years." First impression makes that single line feel like the entire result. Inside, though, four separate identities sit hidden. Wrapping them into one line hides the actual flow. Here's a decomposition of that single number.

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How that single line gets compressed in your head

The biggest text at the top of the result screen displays the final value as one line. "$180,000."

Reading that, the mental processing usually runs like this.

"$180K in 5 years. I put in $100K, so I made $80K — that's about 16% a year, right?"

This single line actually compresses four things at once. How much was the principal? Was it put in upfront or over time? How much was the gain? Was the period 5 years or 7 years? Four pieces combine and compress into one line in your head.

The problem is that compression isn't accurate. Unpacking the one number into its four identities can change how the same result reads.

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Identity ①: How much was actually mine (total principal contributed)

The first thing to separate is total principal contributed. Out of the $180,000 result, how much was purely what you put in.

A trap here. The total for "what I put in" differs completely between running the backtest as monthly DCA and as upfront lump sum.

For example, putting in $1,000 a month for 5 years means total principal of $60,000. Putting in $100,000 upfront once means total principal of $100,000. The same $180,000 result carries completely different meanings.

• $60,000 → $180,000: roughly 3x growth from principal
• $100,000 → $180,000: roughly 1.8x growth from principal

Looks like the same result, but the first one had the asset working harder. The second one less. Looking at the one-line result alone hides the principal — and misses the real efficiency.

That's why the result card's second slot shows total principal separately. With $60,000 principal sitting next to $180,000, the comparison starts in your head.

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Identity ②: So what was the actual gain (cumulative return)

Once principal is separated, the gain portion emerges naturally. $180,000 minus $60,000 principal equals $120,000 in gain. Expressed as a percent of principal, that's about +200%.

Cumulative return matters because "how many times the money I put in" summarizes into one number. Looking only at the account balance, $180,000 looks like a big number — but $60,000 of principal sits underneath and the actual gain is $120,000. Whether that $120,000 is large relative to $60,000 of principal needs the ratio to compare against other assets.

• Final $180K → any asset's number looks big
• Cumulative +200% → if another asset over the same period was +80%, the difference is clear

When comparing to other assets, cumulative return is the most intuitive. Comparing the absolute final value ($180K) directly is hard because principal differs across cases. Cumulative +200% vs +80% compares directly.

That's why the result card's third slot holds cumulative return separately. Pulling it out of the one-line result is where comparison starts.

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Identity ③: What pace was that each year (CAGR — annualized return)

This is where the real distortion begins. Reading cumulative +200%, the mental conversion runs like this.

"+200% in 5 years means +40% a year!"

Wrong conversion. +200% cumulative was built across 5 years. The actual yearly pace required to produce that result needs separate calculation — and that's what CAGR (compound annual growth rate) is.

CAGR is the compound average. The pace that, if held constant each year, would produce the result. Producing +200% cumulative across 5 years requires roughly +24.6% per year on average. Very different from the +40% that simple division gives.

This difference matters because it allows pace comparison against other assets.

• S&P 500's long-term CAGR averages roughly +10%
• A portfolio CAGR of +24% → faster pace than the long-term average
• A portfolio CAGR of +6% → slower pace than the market average

Looking only at the one-line $180K result doesn't tell you whether the asset runs faster or slower than the market average. Reading CAGR separately is when the asset's pace becomes visible.

That's why the result card's fourth slot holds CAGR. Reading it separately from cumulative is what brings the pace into view.

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Identity ④: How long was that period (investment horizon)

The last identity is the period. Whether $180,000 came in 5 years or 7 years completely changes the asset's character.

A natural flow once you think about it. The same result built in less time means the asset ran fast. Built in more time means it ran slow. As the horizon lengthens, the CAGR required to reach the same result drops.

• $100K → $180K, 5 years: about +12.5% annual pace
• $100K → $180K, 7 years: about +8.7% annual pace
• $100K → $180K, 10 years: about +6.1% annual pace

Same result, different time the asset worked. Looking only at the one-line result loses that time entirely. "$180K" reads the same whether built in 5 years or 10 years.

Reading the time alongside is what brings the pace into view. Comparing a 5-year short-term result with a 10-year long-term result on the same scale makes the shorter one look more attractive by default — but the shorter one might not have captured the volatility yet because the data window is short. The longer one might have passed through a large drawdown along the way.

That's why the result screen places the investment horizon next to the result. It's the denominator of the one-line result.

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What changes when you read the four together

Holding all four together, the same $180,000 result organizes into different meaning.

Same $180K, completely different mental organization. The first is just a big number. The second shows the asset's character.

What changes isn't just organization. The same $180K result, decomposed, is one asset running at +24% pace and another at +6% pace. A +24% asset and a +6% asset are nearly different assets, but the one-line result buries that difference completely.

This decomposition is decisive when comparing two assets. A at $180K and B at $150K — A looks better at first glance. But A took 10 years to go $100K → $180K, while B took 5 years to go $70K → $150K. B's pace is much faster. The one-line result never shows that flow.

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How to read the result screen

When reading results, don't stop at one line. Walk through the four identities in order. That's why the result card is laid out across four lines.

One-line result → separate principal → separate cumulative → separate pace (CAGR) → check the horizon

Running this flow through your head once stops the big number from sweeping you away on the next reading. The simple habit of reading principal, cumulative, CAGR, and horizon alongside the one-line result cuts down the "I picked it based on one big number" regret.

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Looking at it directly

Running it directly is the fastest way. Run an asset you're interested in across the same period and watch how principal, cumulative, CAGR, and horizon each print separately next to the one-line result. Walk through the decomposition by hand once, and the next results organize into four lines automatically in your head.

Don't stop at one line. Decompose into principal, cumulative, CAGR, and horizon. The big number stops sweeping you away.

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• This information is not investment advice.
• Past performance does not guarantee future results.
• Backtest results are simulations and may differ from actual trading outcomes.