Does betting a fixed percentage of your bankroll work?

How Fixed fraction (2%) is played

1. Each spin, stake 2% of the current bankroll on red, rounded down to whole dollars (minimum $1).
2. Stakes shrink as the bankroll falls and grow as it rises.

What 20,000 sessions show

Sessions that finished ahead were up $203.53 on average; sessions that finished behind were down $408.80. Almost no session ran out of money or hit the table limit; the losses came from steady erosion instead. 58.2% reached the 500-spin cap without hitting the target or busting.

Proportional staking is sound bankroll management when a bet has positive expectation. On a negative-expectation bet it only controls the speed of decline: shrinking stakes make ruin very unlikely, while the bankroll still trends down by the house edge on everything wagered.

The median session lasted 500 spins. The median longest losing run was 7 spins in a row (the worst of 20,000 was 22), and one session in ten put at least $23 on the table in a single spin.

European versus American wheel

The same 20,000 seeds, replayed on a double-zero wheel. The second zero roughly doubles the edge to $5.26 per $100 wagered. Measured return goes from −$2.69 to −$5.32 per $100, and the mean session from −$142 to −$294.

The code that produced these numbers

This Lua is the strategy as Engineer mode runs it, inside the same sandbox and kernel. A test in the repository replays it against the bulk generator on fixed seeds and fails the build if the two ever disagree by a single dollar.

-- Fixed fraction (2%): stake 2% of the current bankroll on red, every spin.
-- Session rules shared by every 0xroulette.com/systems page:
-- $5 unit, $500 table max, walk away at +$200, and stop the moment
-- the next stake can't be covered by the bankroll or the table limit.
local UNIT, TABLE_MAX, TARGET = 5, 500, 200

local function reset() end
local function settle(result) end

local function place(ctx)
  return { { type = "red", amount = math.max(1, math.floor(ctx.bankroll * 0.02)) } }
end

-- Shared wrapper: enforces the session rules around place/settle.
strategy = {}
local start, stopped

function strategy.setup(ctx)
  start, stopped = ctx.bankroll, false
  reset()
end

function strategy.bet(ctx)
  if stopped or ctx.bankroll >= start + TARGET then
    stopped = true
    return {}
  end
  local bets, stake = place(ctx), 0
  for _, b in ipairs(bets) do
    if b.amount > TABLE_MAX then stopped = true end
    stake = stake + b.amount
  end
  if stake > ctx.bankroll then stopped = true end
  if stopped then return {} end
  return bets
end

function strategy.on_spin(ctx, result)
  if not stopped then settle(result) end
end

Session rules

Limitations

One bankroll, one unit size, one table limit, and one walk-away target. A bigger bankroll or a higher limit moves where a progression breaks; it does not change the return per dollar wagered. Spins are fair and independent, as on a correctly functioning wheel or a certified RNG. Physical wheel bias is a separate question, covered on Physics.

Related

• Does flat betting work at roulette?
• Does the D’Alembert system work?
• Does the Paroli system work?
• Study: Drawdown and ruin methodology
• All 20 systems, compared on the same seeds