Most bettors remember their big wins vividly and forget their steady losses, which is why so many believe they are breaking even while their bankroll shrinks. A spreadsheet fixes that memory bias with facts. It does not need fancy software: a free spreadsheet with one row per bet, a few formulas and a weekly review is enough to reveal whether you have an edge, where it lives, and which habits cost money.

Return on investment, or ROI, is the key number. Divide total profit by total staked and multiply by 100. A bettor who staked 10,000 over a season and profited 500 has a 5% ROI, a solid result that most professionals would respect. Strike rate, the percentage of bets won, matters less on its own, since winning many bets at short odds can still lose money, while winning fewer bets at long odds can profit handsomely.

Start with date, competition, match, market, selection, odds taken, stake, result and profit or loss. Add three columns that turn a log into a learning tool: your reason for the bet in a few words, your estimated probability before the match, and the closing odds at kick-off. Those three columns let you test whether your reasoning works, whether your probability estimates are calibrated, and whether you beat the closing line.

Profit for each row is simple: for a winning bet, multiply stake by odds and subtract stake; for a losing bet, profit is negative stake. Total profit is the sum of that column, total staked is the sum of stakes, and ROI is total profit divided by total staked. Yield by market uses the same formula filtered to one market, such as totals or handicaps, and a pivot table or simple filter gives you that breakdown in seconds.

A spreadsheet will not pick winners for you, but it will tell you the truth about your betting, and the truth is the most valuable tool a bettor owns. Twenty minutes of setup, one minute per bet, and a weekly review will separate you from the vast majority of bettors who never learn from their own results.