How it's worked out
Win rate = deals won / (deals won + deals lost) x 100. Pick a period, count the opportunities that closed in it either way, and leave out the ones still open.
The answer depends on what you count. Deals still open, deals that went quiet, and prospects who decided to do nothing all move it. Count "no decision" as a loss, because you spent the time either way. Pick one rule and keep it, or this quarter won't compare with the last.
Worked example, with made-up figures: this quarter you won 15 deals and lost 45, and 20 more are still open. Won over won plus lost is 15 of 60, so 25%. Put the open ones in too and it's 15 of 80, about 19%. Leave 10 deals that went quiet as open instead of lost, and it reads 15 of 50, so 30%. Same deals, three figures.
You can also work it out by value: dollars won over dollars won plus dollars lost. That's the one to use for pipeline coverage, since big and small deals rarely close at the same rate.
Where it shows up in your week
Win rate is the last step of your funnel, and the steps before it decide how many deals get there. The sales funnel shows your rate at every step from appointment to signed deal, counted from what you log, and names the weakest one. The win rate calculator works out yours three ways, with the deals that went quiet counted as lost.