An odds screen helps you compare quoted prices across operators by converting odds into implied probabilities and removing bookmaker margin so you can see fair prices. Many paid services automate this process, but the underlying math is straightforward and accessible with free calculators and spreadsheets. This article shows a step-by-step approach to building a free oddsjam calculator style workflow. You will learn the conversions, how to remove the vig, where to find basic tools, common mistakes to avoid, and practical examples to paste into your sheet.

You can reproduce the essential functions of a paid odds screen using free calculators and a spreadsheet.

De-vig normalization turns quoted odds into comparable no-vig prices so you can spot real value.

Arbitrage detection requires math plus practical checks for execution risk and limits.

Quick overview: what an oddsjam calculator does and why you might want a free alternative

What users expect from an odds screen

An odds screen converts quoted odds into a common frame, usually implied probability, so you can compare prices across bookmakers and markets without juggling formats. A reliable quick calculation turns decimal, American, or fractional odds into percentage chances that are directly comparable.

That comparison is the core of what people look for when they say oddsjam calculator: a single interface that highlights price differences, flags likely arbitrage, and shows fair prices after removing bookmaker margin.

What is the free alternative to OddsJam?

A free alternative is a combination of online calculators, hedging tools, and a spreadsheet workflow that converts odds to implied probabilities, removes bookmaker margin to produce no-vig odds, and compares fair prices across operators; this reproduces the core functionality of paid odds screens without live aggregation.

When people opt for a free OddsJam alternative they usually want the math and the insights without a subscription, even if that means manual steps such as pasting prices into a spreadsheet or using a free web calculator for single checks.

For novices, the tradeoff is mostly convenience versus transparency: free tools reproduce the same basic calculations but will often require hands-on inputs and simple spreadsheet work to match a paid service workflow.

When a free alternative makes sense

If your needs are occasional price checks, quick de-vig comparisons, or basic arbitrage detection you can get by with free calculators and templates rather than paying for live aggregation and automation. For frequent live monitoring or high-volume scanning you will likely want more automation, but for learning and occasional use free tools cover the core functionality.

Step 1, convert odds to implied probability. For decimal odds divide 1 by the decimal price. For American odds positive values use 100 / (american + 100) converted appropriately, and for fractional odds convert to decimal then follow the same rule. These conversions form the basis for any odds-to-probability workflow and are explained in operator education and reference material.

The core math any oddsjam calculator must perform

Converting decimal, American and fractional odds to implied probability, oddsjam calculator

As a concrete short rule: implied probability from decimal odds is 1 divided by the decimal odd, expressed as a percentage. This single calculation is enough to let you compare two prices on the same outcome from different operators, provided you apply the same conversion across all inputs, as summarized in an industry reference.

Step 2, measure bookmaker margin. Bookmakers typically add a margin that pushes the sum of implied probabilities above 100 percent, a phenomenon sometimes called overround or vigorish. Identifying that summed surplus tells you how much the operator has embedded in the prices and is the key to deriving no-vig probabilities.

For a three-way market, sum the three implied probabilities and subtract 100 percent to get the overround. That overround represents the embedded margin you need to remove before you can compare fair, or no-vig, prices.

Step 3, de-vig to derive no-vig probabilities and convert back to odds. The standard approach is proportional normalization: divide each implied probability by the total implied probability for the market, then multiply by 100 to scale the set to 100 percent. Converting those normalized percentages back into decimal odds gives you the fair no-vig odds for each outcome.

Use short numbered steps in your sheet: 1) convert to implied, 2) sum implieds, 3) normalized implied = implied / sum, 4) fair decimal = 1 / normalized implied. This preserves relative pricing while removing the operator margin and is a common method recommended in educational resources for margin calculation.

Free tools and resources that cover the essentials

Online calculators and hedging tools

There are free web calculators that handle single tasks such as implied probability conversion or hedging stake calculation; these utilities show the core math so you can check a single market quickly without a subscription. For example, no-vig calculators such as the one at TheRundown demonstrate stake allocation and basic payoff math useful when testing price differences.

Use one calculator at a time for single checks, or paste outputs into a sheet when you need to compare multiple operators. Implied probability tools such as GamingToday can help with single-number conversions.

Public templates and spreadsheets you can adapt

Google Sheets and Excel are the most accessible platforms to reproduce an odds screen. A simple sheet can take decimal prices, compute implied probabilities, calculate overround, perform proportional normalization, and show fair no-vig odds. Templates available from community forums or shared spreadsheets are a good starting point and let you modify steps to match the markets you cover.

When adapting a template, keep formula cells visible and use named ranges for inputs so you can paste new prices quickly. That transparency helps when you later add simple automation such as IMPORTXML or manual copy-paste from a chosen price source.

Where to find price feeds and why source matters

Accurate comparisons need consistent timestamps and identical market definitions. Public odds aggregation sites, API demos, and manually copied prices from bookmakers can all work, but verify that the market is the same type and settlement rules match. Mismatched market definitions are a common source of false signals when comparing prices.

For learning and small-scale comparisons use manual capture or a stable public feed; if you move to frequent scanning prefer a consistent API or a controlled browser workflow so you can trust that comparisons are apples to apples.

A step-by-step workflow to reproduce OddsJam-style comparisons with free tools

Collecting and organizing prices

Start by defining the market precisely: teams or players, market type, and settlement rules. Record the timestamp and operator name for each price so you can audit later. For reproducible checks capture decimal prices, or convert them immediately to decimal, to keep the math uniform. See our blog overview for practical setup tips.

Organize captured prices in a simple sheet with columns for operator, decimal odds, implied probability, and a flag for data quality. That last column should note whether the price was traded live, taken from an exchange, or copied from a bookmaker web page so you can assess execution risk later.

Close up minimalist spreadsheet showing decimal odds implied probability summed overround and normalized no vig odds for oddsjam calculator

Use the formula 1 / decimal to compute implied probability for each entry, then sum the entries for the same market to get the market implied total. If the total exceeds 100 percent you are seeing the bookmaker margin in action and can proceed to normalize the probabilities to remove the vig.

A simple check: if the summed implied probability is close to 100 percent there is little margin to remove; if it is well above 100 percent the operator has a larger margin and de-vig normalization will shift the fair odds more noticeably.

Normalize each implied probability by dividing by the summed implied probability for that market, then compute fair decimal odds as 1 divided by the normalized implied. The resulting decimals are the no-vig odds you can use to compare across operators without the distortion of embedded margin.

To compare markets, subtract the fair decimal at one operator from the fair decimal at another or compare the fair implied probabilities directly. Significant differences after de-vig are candidates for further analysis; small differences may be noise from rounding or timing.

Quick calculator to compute summed implied probability from three decimal odds

Use this to check overround before de-vig

How to choose the right free calculator or workflow for your needs

Accuracy versus convenience

If you perform occasional checks a single hedging or implied-probability calculator and a manual spreadsheet give you full transparency and control. For high-frequency scanning you will trade convenience and speed for higher confidence in execution, which is where paid aggregation and automation typically add value.

The UK technical standards emphasize that displayed odds should reflect underlying probabilities closely; use that guidance to judge whether your workflow is representing prices in a way that is fit for your purpose.

Funded Plays Challenges

Open a blank sheet and test it

Automation options and scaling your workflow

Light automation options include spreadsheet functions that fetch public pages, simple scripts that standardize inputs, or browser automation to collect prices. Start with clear, auditable steps and add automation incrementally so you can verify results and avoid silent formula errors.

Regulatory and ethical considerations

Be mindful of local rules when using price feeds or automating interactions with operator sites; transparency and correct market representation are central to responsible practice and to staying within expected technical standards.

Typical mistakes and how to avoid them

Mixing unmatched markets or timeframes

One common error is comparing prices from different market definitions, for example a matchup listed as 'to finish' on one site and 'including extra time' on another. Always confirm the market settlement rules match before comparing prices.

When in doubt, add a column in your sheet that spells out the market definition and reject entries that do not match exactly. This simple check prevents many false positives when scanning for apparent value.

Forgetting to account for margin and round-off effects

Small price differences can be due to rounding or differing implied margin and not to true arbitrage. Running a de-vig normalization and reviewing the normalized numbers reduces false signals caused by these small effects.

Also note that vigorish can make quoted implied probabilities look better than they are at first glance; removing the vig is essential before you call a difference significant.

Treating snapshot price differences as guaranteed opportunities

Finding a price difference is only the first step. Arbitrage requires correct stake sizing across outcomes and rapid execution. Execution risk, stake limits, and timing mean that many apparent opportunities vanish by the time you act on them.

Use hedging calculators and test stake plans in a dry run to see if a snapshot difference translates into an executable trade once fees, limits, and timing are considered.

Example inputs: Operator A offers 1.90 on Team X and 2.05 on Team Y. Operator B offers 1.88 on Team X and 2.10 on Team Y. Step 1, compute implied probabilities: for 1.90 implied is 1/1.90, for 2.05 implied is 1/2.05, and so on. Step 2, sum implieds per operator to see the overround. Step 3, normalize each implied probability by dividing by the sum, then convert back to decimal with 1 over normalized implied to get fair no-vig decimals. Paste those results side by side to compare fair odds across operators and see where the relative differences lie.

This exercise shows how small differences in quoted prices map to different fair odds once margin is removed, and it demonstrates a simple way to do side-by-side comparisons in a spreadsheet using built-in division and reciprocal functions.

Try a quick de-vig example

Try copying the two-outcome steps into a blank sheet and run the normalization on a pair of prices you care about to see how de-vig shifts the relative value.

Open a blank sheet and test it

Three-way market example (soccer match or similar)

For a three-way market, compute the implied probability for each of the three quoted decimals, sum the three implieds to get the market total, then normalize each implied by that total to get the no-vig probabilities. Convert normalized probabilities back into decimal odds using 1 divided by each normalized probability to get fair decimals for home, draw, and away.

This proportional normalization preserves the pricing relationships while removing the operator margin, which is especially useful in markets with a clear favorite where the margin can distort perceived value.

Simple arbitrage detection walkthrough

Arbitrage exists when you can allocate stakes across outcomes such that combined implied probabilities across operators fall below 1.00 when you apply the correct no-vig comparison. A quick check is to take the best available fair implied probability for each outcome across operators and sum them; if the sum is less than 1.00 there is a mathematical arbitrage candidate, though execution concerns remain.

Before acting on any arbitrage candidate compute stake sizes with a hedging calculator and confirm that operator limits, minimum stakes, and timing permit the trades. Hedging calculators are available for free and are useful to test whether an identified spread can be converted into an executable plan.

Next steps, safe practices and further reading

Checklist before you trade or hedge

Before you place any trades verify: market definitions match, timestamps are recent, commission or fees are accounted for, and the stake sizing plan fits operator limits. This checklist reduces the risk that a seemingly profitable difference fails at execution.

Keep a short audit log for each candidate trade noting prices, calculated fair odds, stake plan, and whether the trade was completed so you can learn from wins and misses under consistent conditions. Read more on how our evaluations work to structure that log.

Where to learn more about odds math

Operator education pages and financial reference guides explain the underlying calculations for implied probability and margin removal. For hands-on work try a hedging calculator and step through a couple of test scenarios in a sheet to reinforce the formulas and the order of operations. See Funded Plays resources for related material.

Reading reliable guides and practicing with known examples helps you move from theoretical understanding to quick, repeatable execution in your chosen workflow.

Short glossary of key terms

Implied probability, the percentage chance implied by quoted odds. Overround or vigorish, the bookmaker margin that pushes summed implied probabilities above 100 percent. De-vig, the process of normalizing probabilities to remove the margin and derive fair no-vig odds. Arbitrage, a set of prices across operators that allow a covering allocation to lock in profit before execution costs and limits. Keep this glossary handy as you build and test your spreadsheet routines.

What is an oddsjam calculator?

It is a tool or workflow that converts quoted odds to implied probabilities, removes bookmaker margin to get no-vig odds, and highlights price differences across operators.

Can I find true arbitrage with free tools?

You can identify mathematical arbitrage candidates by comparing no-vig prices, but execution risk, limits, and timing mean many candidates are not practically executable.

Do free calculators replace paid aggregation services?

They replicate the core math and are great for learning or occasional use, but they lack live aggregation and automation that paid services provide.

Free tools let you understand and replicate the core calculations behind paid odds screens, but doing so responsibly requires consistent inputs, careful execution checks, and repeated practice. Use the methods here as a safe way to learn odds math and test simple comparisons before deciding whether you need paid automation. If you decide to scale up, add measured automation step by step and keep audit trails so you can trace results back to inputs and assumptions.