Roblox simulator economy

Choose the economy's numbers with a pacing table before writing gameplay code, then implement them so the server owns every amount. Code targets Luau on Roblox's rolling platform APIs; the bundled scripts are pure Luau and were run with Lune 0.11.0, outside Studio.

When to use

• Picking or reviewing baseCost, costGrowth, rebirth requirement and multiplier, or offline cap and efficiency values for a simulator, tycoon, clicker, or idle game.
• Writing upgrade, buy-max, currency, rebirth, or offline-earnings code in Luau.
• Displaying large numbers, or values above about 1e15 that lose precision.
• Adding eggs, crates, or spins bought with Robux, or with currency that can be bought with Robux.

When not to use: DataStore reads, writes, session locking and retries → roblox-datastores. Remote protocol design and rate limiting in depth → roblox-networking. Shop and HUD layout → roblox-ui + game-ui-ux. A wave-defense economy → tower-defense. Engine-neutral save format questions → save-systems.

Workflow

1. Inspect. Find where currency, upgrade, and rebirth values live now and which scripts change them. List every RemoteEvent that touches currency and what each one sends.
2. Write the numbers as one config table: base income; each upgrade's baseCost, costGrowth, effect, and maxLevel; rebirth baseRequirement, requirementGrowth, multiplierPerRebirth; offline maxHours, efficiency. Server and client both read it.
3. Run the pacing calculator from the skill directory (paths are relative to it): lune run scripts/balance.luau --print-defaults > economy.json, edit the file, then lune run scripts/balance.luau economy.json. Read the wait and vs prev columns and tune until they match the targets below. --help lists every field and its allowed range; a missing file, invalid JSON, or out-of-range field prints an error and exits 1.
4. Implement on the server with the patterns below and references/server-patterns.md. Copy scripts/economy_math.luau unchanged into a ModuleScript so the maths you tested is the maths that runs.
5. Verify. lune run scripts/test_economy_math.luau (exits 1 on failure) for the maths; a Studio playtest with Server & Clients for purchases, rebirth, leaving and rejoining, and invalid remote arguments.

Formulas

Quantity	Formula	Notes
Price of the next level	floor(baseCost * costGrowth ^ owned)	1.07-1.15 for upgrades bought many times; 1.5-3 for rare large ones
Cost from level a to b	baseCost * g^a * (g^(b-a) - 1) / (g - 1)	Players pay the floored per-level sum, slightly less
Buy max	walk real prices until the next exceeds the balance or maxLevel	Safer than the log formula with floored prices
Rebirth requirement k	baseRequirement * requirementGrowth ^ k
Rebirth multiplier	1 + k * multiplierPerRebirth	Additive grows slowly; multiplicative (q ^ k) grows exponentially
Offline income	floor(min(away, maxHours * 3600) * rate * efficiency)	Away time of 0 or less (clock went back) pays 0

Derivations, the rebirth wait-ratio formula, and a worked example: references/formulas.md.

Pacing targets (starting points, not rules)

• Early upgrades take seconds. In the default config the first 10 levels take 3-10 s each.
• Each rebirth should take only a little longer than the last, for example x1.2-x1.5. The calculator's vs prev column is that ratio. With an additive multiplier it approaches requirementGrowth over time, so requirementGrowth = 3 gives x2.0 rising to x2.7 and rebirth 8 takes 137 days at the default income. requirementGrowth = 1.8 gives x1.2 rising to x1.6.
• Offline earns less than online. An efficiency of 0.25-0.5 and an 8-12 hour cap keep playing worth more than idling without zeroing out players who log off.

Server-owned purchases

A RemoteEvent carries what the player wants ("buy upgrade Income"), never an amount or a price. The server looks up the price, checks the balance, spends, and grants without yielding in between.

-- ServerScriptService/Economy.server.luau (excerpt; full version in references/server-patterns.md)
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local EconomyMath = require(ReplicatedStorage.Shared.EconomyMath)
local Config = require(ReplicatedStorage.Shared.EconomyConfig)

ReplicatedStorage.Remotes.BuyUpgrade.OnServerEvent:Connect(function(player: Player, upgradeId: unknown)
	local session = sessions[player]
	if not session or type(upgradeId) ~= "string" then return end
	local upgrade = Config.upgrades[upgradeId]
	if not upgrade then return end -- unknown id
	local owned = session.levels[upgradeId] or 0
	if owned >= upgrade.maxLevel then return end
	local price = EconomyMath.levelCost(upgrade.baseCost, upgrade.costGrowth, owned)
	if EconomyMath.trySpend(session.wallet, { [upgrade.currency] = price }) then
		session.levels[upgradeId] = owned + 1
	end
end)

• trySpend checks every currency in a multi-currency cost before subtracting any, and rejects negative or non-finite costs.
• Rebirth on the server: compare the server's balance with the requirement, then reset wallet and levels and increment the count. Never accept "I rebirthed" or a balance from the client.
• Rate-limit each remote per player with a token bucket (roblox-networking).

Save data and offline time

• Repair on load; never error. Use sanitizeAmount (non-numbers, NaN, infinity and negatives become 0; fractions are floored) and sanitizeLevel (also clamps to the current maxLevel). Drop unknown upgrade ids and return a list of what was repaired, so old versions and edited data load cleanly.
• Never save NaN or infinity. A division by zero that reaches the wallet should be caught by the same sanitizers before saving.
• Offline time comes from the server clock only: save os.time() on the server when the player leaves; on join, away = os.time() - lastSeen. A missing or future lastSeen counts as now, which pays nothing.
• Precision: Luau numbers are doubles, exact for integers up to 2^53 (about 9e15). If balances can pass about 1e15, store a mantissa/exponent pair or a base-10 logarithm instead.

Big-number display

EconomyMath.formatNumber(value, decimals?) uses the suffixes K, M, B, T, Qa, Qi, Sx, Sp, Oc, No, Dc, Ud, Dd, Td, Qad, Qid, Sxd, Spd, Ocd, Nod, Vg (1e63), then scientific notation.

• The rollover bug: 999950 / 1000 = 999.95, which rounds to "1000.0K". Round first; if the rounded value reaches 1000, move to the next suffix ("1.0M"). The tests cover this case.
• Format on the client for display only; never parse a formatted string back into a number.

Paid random items (eggs, crates, spins)

Roblox's paid random items guidelines apply when a random item is bought with Robux, directly or through in-game currency bought with Robux. Per that page:

• Show every possible outcome and its actual numerical odds, as percentages that sum to exactly 100%, before purchase (long decimals may be rounded, with a note that the shown total may not be exactly 100%).
• Probability modifiers such as luck boosts and pity systems are covered: explain their effect numerically before purchase, and update the shown odds live while a boost is active.
• If the full list does not fit, open it from a control labelled "Info" or "Details" that is visible before purchase; an "(i)" icon without a word is not enough.
• PolicyService:GetPolicyInfoForPlayerAsync() returns ArePaidRandomItemsRestricted; for those players, apply one of the treatments the page lists.

Build the odds panel with EconomyMath.oddsPercent(outcomes) and roll on the server with EconomyMath.pickWeighted(outcomes, rng:NextNumber()) from the same list (after applying any boost), so shown and actual odds cannot drift.

Pitfalls

• Rebirth 6 takes weeks → requirementGrowth far above the multiplier's growth; read the vs prev column and lower requirementGrowth or switch to a multiplicative multiplier.
• Prices outrun income after ~20 levels → costGrowth of 1.5+ on an upgrade meant to be bought 50 times (level 50 costs about 637 million times level 0); use 1.07-1.15.
• Late game breaks after a few rebirths → multiplicative multiplier (1.5 ^ k) without a matching requirement curve; keep requirementGrowth / q near the ratio you want.
• Players gain currency they did not earn → a remote accepts an amount or price, or the check happens only on the client; send ids, price on the server.
• Two purchases pass one balance check → the handler yields between check and spend; spend before any task.wait, DataStore call, or other yield.
• Buy max freezes the server → uncapped loop or a price of 0; pass maxLevel, keep baseCost >= 1 (maxAffordable errors instead of looping forever).
• Offline pays days of income → client timestamp, no cap, or a corrupted lastSeen; use the server clock, cap, and treat future times as now.
• HUD shows "1000.0K" → math.floor(x * 10) / 10 before choosing the suffix; use formatNumber.
• A save fails or loads as garbage → NaN or infinity reached the wallet; sanitize before save and on load.

Resources

• scripts/balance.luau — pacing calculator: per-level price, total, income and wait; per-rebirth requirement, multiplier, wait and ratio; offline maximum. Run with --help first.
• scripts/economy_math.luau — the formulas, trySpend, sanitizers, odds and formatNumber as pure Luau; runs in Lune and in a Roblox ModuleScript.
• scripts/test_economy_math.luau — tests for every function (lune run, exits 1 on failure).
• references/formulas.md — derivations, rebirth ratio, worked example.
• references/server-patterns.md — config layout, income tick, buy max, rebirth, load repair with offline income, and paid random item rolls.

Related skills

• roblox-luau — services, ModuleScripts, and the client/server split.
• roblox-networking — remote validation and token-bucket rate limits.
• roblox-datastores — loading and saving the session this skill repairs.
• roblox-ui — shop, upgrade, and odds panels.
• roblox-studio-workflow — Server & Clients playtests.

Primary references

• https://create.roblox.com/docs/production/monetization/paid-random-items
• https://create.roblox.com/docs/scripting/events/remote
• https://create.roblox.com/docs/scripting/security/client-server-boundary
• https://create.roblox.com/docs/reference/engine/classes/PolicyService
• https://create.roblox.com/docs/reference/engine/datatypes/Random
• https://lune-org.github.io/docs