Weekly Returns Calculator

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Turn four individual weekly returns into a monthly and an annualized return, with the compounding handled correctly. Instead of forcing you to average your weeks by hand, this calculator takes each week separately — exactly how trading logs, portfolio snapshots, and side-project revenue actually arrive — and compounds them: (1+w₁)(1+w₂)(1+w₃)(1+w₄) − 1 for the month, then your geometric average week grown over a 52-week year for the annualized figure. That distinction matters, because weeks of +10% and −10% do not cancel out: they compound to a loss, and a simple average would hide it. The tool also reports your geometric average weekly return — the single constant weekly rate that would reproduce your month — which is the honest number to compare against other strategies. Losses work naturally: enter negative percentages down to −100%. Everything runs entirely in your browser — nothing you type is uploaded — so it is private, instant, and works offline. Pair it with the Interest Rate Converter above when you want to translate a single rate between periods instead.

Enter all four weekly returns to see the monthly and annualized results.

The four weeks compound into the monthly return: (1+w₁)(1+w₂)(1+w₃)(1+w₄) − 1. The annualized figure compounds your average week over a 52-week year, so it assumes future weeks perform like these four. Returns compound — four weeks of 1% make 4.0604% monthly, not 4%.

How to use

Type each week's percentage return into its own box — for example 2.5 for a week that gained 2.5%, or -1.2 for a week that lost 1.2%. As soon as all four boxes hold valid numbers, the results appear: the monthly return (your four weeks compounded in sequence), the annualized return (your average week compounded over 52 weeks), and the geometric average weekly return. Each result has a copy button. Rates can be negative down to -100%; anything lower is rejected because you cannot lose more than everything in a week.

Frequently asked questions

Why is my monthly return not just the sum of the four weeks?
Because returns compound: each week's gain or loss applies to the balance the previous weeks left behind. Four weeks of +1% grow your money by 1.01 × 1.01 × 1.01 × 1.01 − 1 ≈ 4.0604%, slightly more than the naive 4%. The effect is much starker with losses: +10% followed by −10% leaves you at 0.99 of where you started, a 1% loss, even though the simple sum is zero. That is why the calculator multiplies growth factors instead of adding percentages.
How is the annualized return calculated?
The four weeks are compounded into a single 4-week growth factor, and that factor is raised to the power 13 — because a 52-week year contains thirteen 4-week blocks. Equivalently, your geometric average weekly return is compounded 52 times. Note this is an extrapolation: it assumes the rest of the year performs like the four weeks you entered, so treat it as a what-if projection rather than a guarantee. Also note it intentionally uses a 52-week year rather than compounding the monthly figure 12 times, which would only cover 48 weeks.
What is the geometric average weekly return for?
It is the single constant weekly rate that would reproduce your exact 4-week result — the fourth root of your total growth factor, minus one. It is always at or below the simple arithmetic average, and the gap widens the more volatile your weeks are; this drag is exactly why erratic returns underperform steady ones. Use it to compare volatile strategies fairly, or to feed a single representative rate into the Interest Rate Converter. All calculations happen locally in your browser and nothing is sent to a server.