Free tool

Tennis trading profit calculator

Updated on 21 October 2026Free, no sign-up

Enter your stake and the price you buy at, then choose how the trade ends: you sell at a price, your player wins, or your player loses. You'll see how many shares you get, your profit or loss, your return, and the price you need to break even.

How it works it out

Shares are your stake divided by the buy price. $50 at 62¢ buys 80.65 shares.
If you sell, you get shares × sell price. 80.65 shares at 72¢ is $58.06.
If your player wins, each share pays $1, so you get $80.65.
If your player loses, the shares pay nothing.
Profit or loss is what you get back minus your stake, and the return is that as a percentage of your stake.
Break-even is the sell price at which you get your stake back. With no fees, it's simply the price you paid.

About the fee field

Real markets cost money to trade. When I checked in October 2026, Polymarket charged a fee on tennis trades that fill straight away, and the amount depends on their current fee schedule. The fee field here is a simplification: it takes a flat percentage off each buy and each sell. That's enough to see how costs push up your break-even price. For exact numbers, check Polymarket's fee page. The 77 Tennis demo has no fees, so leave it at 0 to match.

Worked examples

Trade	Shares	Back	Profit or loss	Return
$50 at 62¢, sell at 72¢	80.65	$58.06	+$8.06	+16.1%
$50 at 62¢, player wins	80.65	$80.65	+$30.65	+61.3%
$50 at 62¢, player loses	80.65	$0.00	-$50.00	-100%
$20 at 35¢, sell at 50¢	57.14	$28.57	+$8.57	+42.9%
$100 at 80¢, sell at 70¢	125	$87.50	-$12.50	-12.5%

Cheap prices aren't cheap

Buying at a low price gives you a big return if it works, but it works less often. A 20¢ player should win about one match in five if the price is right. Over many trades, a cheap price and an expensive one can be equally fair. The question is always whether the price is too low for the real chance, not whether it looks cheap. How tennis prices work explains why.

Before you place a trade, decide where you'd sell. Take-profit and stop-loss for tennis trading shows how to pick those levels, and this calculator tells you what each one is worth.

FAQ

Why is the break-even price the same as my buy price?

With no fees, selling at the price you paid gives you your stake back. Add a fee and the break-even price goes up, because you pay on the way in and on the way out.

Can I lose more than my stake?

No. When you buy shares, the worst case is that they end up worth nothing and you lose your stake.

Does this work for any prediction market?

The maths works for any market where a winning share pays $1, which is how Polymarket's tennis markets work. Fees differ between platforms.

How many shares do I need on Polymarket?

The tennis markets I checked in October 2026 had a minimum order of 5 shares. The 77 Tennis demo has a $5 minimum per trade instead.

Demo only. 77 Tennis uses demo money with no cash value. Nothing here is financial or betting advice. Prices come from Polymarket's public tennis markets, and I'm not affiliated with Polymarket. Prediction markets aren't legal everywhere, so check the rules where you live. If trading stops being fun, stop.