i What this calculator does
Quick answer: The rand fell against the dollar: rand weakness or dollar strength. With the default inputs (USD/ZAR change over the period 3, EUR/USD change -1.5), it returns rand vs the trade-weighted basket of +1.98%.
When USD/ZAR rises 3% in a month, the headline says the rand fell. Often half of that is the dollar rising against everything. This calculator takes the percentage moves of five rates over your period, builds the rand's move against a trade-weighted basket of the euro, yuan, dollar, pound and yen, and splits the USD/ZAR move into the part that was the rand and the part that was the dollar.
The default weights approximate the SARB's trade-weighted index and can be edited. The currency strength calculator ranks currencies against each other; this tool answers the specifically South African question that the rand weakness article raises, in one sentence you can quote.
This calculator is for educational purposes only. Results are estimates and may vary depending on market conditions, spreads, commissions, platform settings, and exchange rates. It should not be considered financial advice.
Common results
What the calculator returns as the USD/ZAR change over the period changes, with every other input at its default (EUR/USD change -1.5, GBP/USD change -1, USD/CNY change 0.8, USD/JPY change 2, basket weight: euro 33, basket weight: yuan 28, basket weight: dollar 20, basket weight: pound 10, basket weight: yen 9).
| USD/ZAR change over the period | Rand Vs The Trade-Weighted Basket | Dollar Strength Component | Rand Weakness Component |
|---|---|---|---|
| 1.5% | +0.49% | +1.01% | +0.49% |
| 2.5% | +1.48% | +1.02% | +1.48% |
| 3% | +1.98% | +1.02% | +1.98% |
| 4% | +2.97% | +1.03% | +2.97% |
| 5% | +3.96% | +1.04% | +3.96% |
| 7.5% | +6.43% | +1.07% | +6.43% |
Figures used in this calculator
The South African constants this calculator relies on, with the page that holds the current value and the date it was last verified.
- SARB reference rates: Published daily for USD, EUR, GBP. Source: Rand Exchange Rate History (verified 27 September 2026).
- Repo rate: 7.25%. Source: SARB Repo Rate History (verified 27 September 2026).
How the calculation works
The calculator takes two inputs: Win Rate and Number of Trades to Analyse. The expected longest streak is log(N × WinRate) ÷ log(1 ÷ LossRate) ≈ 6.4 trades. Based on random, independent trade outcomes at a fixed win rate, an approximation, not a guarantee. The breakdown also lists 3+ losses in a row, 5+ losses in a row and 7+ losses in a row.
A worked example in rand
With the default inputs (win rate 45% and number of trades to analyse 100), the calculator returns a expected longest losing streak of 6.4 trades, over 100 trades. It also reports chance of 5+ in a row 91.2%, chance of 10+ in a row 10.0% and loss rate 55.0%. Double the win rate to 90 and the expected longest losing streak moves from 6.4 trades to 2.0 trades, the chance of 5+ in a row moves from 91.2% to 0.1% and the chance of 10+ in a row moves from 10.0% to 0.0%.
How to read the result
The headline figure is the expected longest losing streak; the others are there to show where it came from. A 20% drawdown needs a 25% gain to recover and a 50% drawdown needs 100%, so the figure to watch is not the loss but the recovery it demands; most professional accounts treat 20% as the point at which size is cut. The background to this calculation is in Can I Switch Brokers Without Losing My Trading History?.
The South African angle
Three things change the picture for a South African trader using the losing streak calculator. Monte Carlo simulation of a strategy's trade sequence is the standard way to estimate how deep a drawdown it can produce, and most South African retail accounts have never run one. A rand account that funds dollar instruments shows a drawdown when the rand strengthens even if every trade is flat, which is why the currency should be checked before the strategy is blamed. SARS does not allow a trading loss to be set against salary income unless trading is your trade, so a drawdown is also a tax event with no immediate offset for most part-time traders. The figures behind these points, and the ones the losing streak calculator itself uses, are on the South African forex trading statistics.
Why a basket, and whose weights
A currency can only be measured against other currencies, so "the rand fell" always means "against something". Against the dollar alone, the rand's move mixes two things: what happened to the rand and what happened to the dollar. A trade-weighted basket, weighted by how much South Africa trades with each currency area, removes the second: if the rand fell 3% against the dollar but only 1% against the basket, two thirds of the headline was the dollar. The default weights approximate the SARB's nominal effective exchange rate: euro area and China dominate South Africa's trade, the United States is third, then Britain and Japan.
How to use it with real data
Take the percentage changes of the five rates over the period you care about, a day, a month or a year, from any charting platform, and enter them with the sign conventions shown next to each field. The SARB publishes the actual nominal effective exchange rate monthly, which is the figure to compare the basket result against; the rand exchange rate history carries the dollar series, and the dollar index article explains the index that measures the dollar side of the same question.
What the split tells a trader
If a USD/ZAR move was mostly dollar strength, the rand will usually give it back when the dollar turns, and the better trade is in the dollar against other currencies rather than in the rand. If it was mostly rand weakness, the driver is local: the MPC, the Budget, Eskom, a ratings review, or an emerging-market sell-off that hit the rand with its peers, and the rand crosses, EUR/ZAR and GBP/ZAR, will show the same move. The rand weakness article shows how the two kinds of episode have differed in the rand's history.
Spotted an outdated figure? If a rate, limit or formula in this calculator no longer matches its source, email us the page and the source. A material correction is dated on the Updates Log.
Frequently asked questions
Why does EUR/ZAR move by (1 + USD/ZAR) × (1 + EUR/USD) − 1?
Because EUR/ZAR is USD/ZAR multiplied by EUR/USD. If the dollar rises 3% against the rand and the euro falls 1.5% against the dollar, the euro rises about 1.45% against the rand, not 1.5%.
Where do the default weights come from?
They approximate the trade weights the SARB uses in its nominal effective exchange rate, collapsed to five currencies and renormalised. Edit them if you want the Reserve Bank's current published weights or your own.
Can the dollar component exceed 100% of the move?
Yes. If the dollar rose against everything and the rand actually gained against the basket, the dollar component is larger than the whole USD/ZAR move and the rand component is negative. The summary flags that case.
Does this work for a day as well as a year?
Yes, with the same inputs over the shorter period. On single days the dollar component is often dominant around US data releases, and the rand component around SARB decisions.
Why are commodity prices not in the model?
Because this is a decomposition of exchange rate moves, not an explanation of them. Gold and platinum prices are a reason the rand component moves; they are not a currency in the basket.
How does this relate to the dollar index?
The dollar index measures the dollar against six developed-market currencies; the dollar component here measures it against the rand's own trading partners, which include the yuan. They usually agree in direction and differ in size.
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