Does the turnover figure mean I lose that much?

No. Turnover is the total of your stakes, and winnings get restaked as you go. The expected cost is roughly the turnover multiplied by the house edge, which is what the calculator shows separately.

What is the wagering base?

Whether the multiplier applies to the bonus alone or to your deposit plus the bonus. On a 100% match, choosing deposit plus bonus doubles the turnover required for the same headline number.

Bonus wagering calculator

A bonus is worth what you can withdraw from it, not what it says on the banner. Put an offer in below and you'll see how much you'd have to stake to clear it, and what that staking is likely to cost.

The offer

Currency

Your deposit

Match %

Maximum bonus

Wagering

Game RTP %

Wagering applies to

This is the one people miss. On a 100% match, switching to deposit plus bonus doubles the staking for exactly the same headline.

What it costs

Bonus you receive: £100
You must stake: £3,500
Expected cost of that staking: £140
Turnover per 1 of bonus: 35.0x

Clearing this is expected to cost £40 more than the bonus is worth. On average you would finish behind by taking it.

Staking £3,500 doesn't mean losing it. Winnings get restaked as you go, so the cost is roughly the turnover multiplied by the house edge, which at 96% RTP is 4.0%.

What this leaves out

Game weighting. If a game contributes 10% toward wagering, the real staking is ten times the figure above. Slots usually count in full; table games often don't.
Maximum conversion. Many offers cap what bonus winnings can become withdrawable cash, sometimes well below the bonus itself.
Variance. These are averages over a lot of spins. Any single attempt can finish a long way either side of them.
Time limits and max bet rules. An expiry you can't meet, or one bet over the cap, can void the whole thing.

None of this makes a bonus profitable. The house edge applies to every pound of that turnover, which is why the expected cost is always a loss. What the arithmetic does tell you is which of two offers costs less to clear. How wagering requirements work goes through it properly.