i What this calculator does
Quick answer: Your bot adds a bigger position every 200 pips against you. With the default inputs (account equity 50 000, leverage 100), it returns levels the account survives of 7.
Grid and martingale systems, the engine inside most expert advisors sold to retail forex traders, add to a losing position at fixed intervals, often with a larger lot each time, and close everything when price returns. They win small amounts often and lose everything once. This calculator shows where "once" is: enter the account, leverage, starting lot, multiplier, level spacing and the pair's volatility, and it returns the number of levels the account can absorb, the total adverse move that triggers the margin call, the drawdown at each level, and how often the pair has historically moved that far without coming back.
It is the arithmetic the martingale article describes, applied to your own settings. If you are evaluating a bot, run its parameters here before running it on a live account; the article on expert advisors covers the rest of the due diligence.
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 account equity changes, with every other input at its default (leverage 100, starting lot size 0.1, lot multiplier per level 1.5, spacing between levels 200, maximum levels the bot will open 10, pip value per standard lot 10, contract value per lot 1 850 000, stop-out level 50, pair).
| Account equity | Levels The Account Survives | Adverse Move That Ends It | Chance Of That Move In A Month |
|---|---|---|---|
| R15 000 | 4 | 800 pips | 46.0% |
| R25 000 | 5 | 1 000 pips | 45.0% |
| R50 000 | 7 | 1 400 pips | 43.1% |
| R100 000 | 9 | 1 800 pips | 41.1% |
| R200 000 | 10 | 2 275 pips | 38.8% |
| R400 000 | 10 | 4 040 pips | 30.7% |
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.
- Negative balance protection: Offered by most FSCA-licensed brokers, not a legal requirement. Source: Leverage and Margin Limits Reference (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.
How a grid dies
Each level adds lots, so the floating loss grows faster than the move: at level 5 of a 1.5× martingale with 200-pip spacing, the position holds about 13 times the starting lot and has lost on four of its five entries. Margin required grows with the open lots while equity shrinks with the loss, and when equity falls to the stop-out share of margin the broker closes everything at the worst point. The table shows that path level by level; the calculator finds the first level at which it happens and converts the distance into a percentage move of the pair.
Why the probability is the real number
A grid that survives 1,400 pips on USD/ZAR sounds robust until you see that 1,400 pips is 0.76% of the rate, and the pair moves that far in a single direction on most trading days. The calculator uses the pair's volatility to estimate how often a one-directional move of the wipe-out size occurs in a month and in a year, with a normal distribution that understates it: real currency moves trend and gap, which is exactly what kills grids. The 2015 rand flash crash, the March 2020 move and several SARB surprises each exceeded a typical retail grid's range in hours.
What to do with the result
If the monthly probability is above a few percent, the system's equity curve is a series of small gains followed by a total loss, and its backtest looks good only because the test period did not include the move. Three settings change the outcome: a smaller starting lot, a multiplier of 1, and a hard maximum number of levels with a stop beyond it, which turns an unlimited loss into a defined one. The risk of ruin calculator shows what a defined loss does to an account instead; the expectancy calculator shows why a strategy that cannot lose big rarely wins big.
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
What is the difference between a grid and a martingale?
A grid adds equal lots at fixed intervals; a martingale multiplies the lot at each level, classically doubling. Set the multiplier to 1 for a grid and 2 for a pure martingale. Most sold expert advisors use something in between, like 1.3 to 1.7.
Why does the margin level fall so fast?
Because two things move against you at once: the floating loss reduces equity and the added lots increase the margin required. Margin level is the ratio of the two, so it collapses faster than either alone.
Does a bigger account solve the problem?
It moves the wipe-out further away; it does not remove it. Doubling the account roughly adds one level to a 2× martingale. The probability of the fatal move falls, but the loss when it comes doubles.
Why does the model say the real probability is higher?
Currency moves are not normally distributed and they trend, so a run in one direction is more common than the model assumes, and gaps on Monday opens or news releases skip levels entirely. The figure here is a floor.
What volatility should I enter?
The pair's realised annual volatility, roughly 15% for USD/ZAR, 7% for EUR/USD, 8% for GBP/USD, 15% for gold. Volatility rises in stress, which is when grids die, so testing at a higher figure is prudent.
My bot has made money for eight months. Does this still apply?
Yes. Eight months of small wins is exactly what a grid produces before the move that ends it. The calculator shows how likely that move is in any given month; eight months without it is not evidence that it will not come.
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