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Overlaying and underlaying in matched betting

This post explains all about overlaying and underlaying in matched betting.

Lay slightly more (overlaying) or slightly less (underlaying) to ensure a risk-free matched bet.

Use Trickybet advanced calculator to calculate standard matched bet lay stakes, overlays and underlays.

What is overlaying?

When matched betting, you place a specific lay bet stake to give equal profit on all outcomes. Let’s call this a standard lay bet.

Overlaying is laying more than a standard lat stake at a betting exchange.

By overlaying you win more money at the exchange if your lay bet wins, but make less profit if your back bet wins at the bookmaker.

Overlaying example

Overlays are useful for free bet on winner horse racing offers.

Let’s imagine a £10 bet at 5/1 (6.0) for Betfair Sportsbook 3/1+ SP winner offer.

Your horse is 6.0 lay odds at Smarkets.

The standard lay stake is £10.03 (at 2% exchange commission) for 17p qualifying loss.

Alternatively, lay £10.20 (overlaying) on Smarkets to make this offer risk-free.

If your horse wins: The overlay gives £1 qualifying loss, but with £10 free bet to come.

If your horse loses: No free bet is due. However, the overlay ensures £0 qualifying loss. Your £10.20 lay covered the exchange commission on your winning lay bet.

A standard lay stake would give a qualifying loss. Therefore, overlaying is used to eliminate risk when matched betting.

What is underlaying?

Underlaying is the opposite of overlaying. Underlaying a bet means laying less than the standard amount. The underlay makes the matched bet risk-free with a bigger potential win.

The potential outcomes are:

  • If your back bet wins – you make more profit.
  • Back bet loses – your profit is less than a standard matched bet.

To ensure a risk-free bet offer is 100% risk-free, underlay at the exchange.

Underlaying a free bet refund offer

For example, a £10 risk-free bet on 3.0 odds/3.10 lay odds.

The standard of £9.74 = £0.45 loss and the offer isn’t risk-free.

Underlay of £ 9.52 gives zero loss if win, or £0.67 loss if doesn’t win.

You only receive a free bet if your selection loses, so underlay to either:

  • a) break-even if win, or
  • b) small loss (-£0.67) if lose but with £10 free bet to come.

Assuming your £10 free bet is converted to £8 profit, your overall risk-free profit is £7.

Underlaying a free bet

Matched bettors often underlay Stake Not Returned (SNR) free bets used at high odds.

Imagine a £10 free bet on 10.0 back odds/10.0 lay odds. Lay £7 at the exchange (2% commission).

  • If the free bet wins £27 profit (£90 win minus £63 lay bet loss).
  • Free bet loses £6.86 profit.

Underlaying will make an extra profit if your high odds selection wins, whilst sacrificing a small portion of your free bet.

Underlaying for bonus offers

Underlaying is useful for bonus rollover offers. Underlay to try to lose your bookmaker balance to the exchange.

Otherwise, if your back bet wins, you’ll have enough money at the bookie to complete the wagering.

Underlaying arbitrage bets

Underlaying is also useful when matched betting in shops.

Discover arb bets on shop betting coupons, then lay your stake plus commission. This gives a risk-free shot at making profit.

See the sharbing guide for examples of underlaying.


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