Theme parks can be an expensive day out, but there are ways to cut the cost and get cheaper entry.

If you think you’ll be visiting one or more parks a lot over the course of the year, an annual pass can offer a good saving. A Merlin pass offers unlimited entry to theme parks and attractions including Alton Towers, Thorpe Park, Chessington World of Adventures and Legoland.

Here are some other top tips.

Buy online in advance

Generally speaking, you can save money by booking online in advance. For example, at Chessington World of Adventures, if you book more than five days in advance, early bird tickets are available from £27.

If you book between one and four days ahead it’s £32 per ticket, and if you show up on the day it’s £47. So a bit of forward planning could save you up to £20 on each visitor at this park.

The earlier you book the more you’re likely to save.

[Related story: How to save money on your food shopping]

Look for discount codes, vouchers and cashback

Don’t jump straight in and book without taking a look around for two-for-one vouchers and other discounts. Search engines are your friend here.

There’s no definitive source for discounts, so if you’re planning a day out, be sure to search for vouchers and promo codes when you book to make the most of seasonal offers.

One website you might like to keep an eye on is myfamilyclub.co.uk which catalogues some decent theme park deals. But do your own research and see what else is out there too.

Also remember to check for cashback offers before you commit. Quidco is currently offering £5 cashback on annual passes for Legoland Windsor, while TopCashback is offering £5.25.

Look out for promotions

There are regular promotions for the bigger theme parks available on everything from frozen food to cereal packets.

Birds Eye is currently running an on-pack promotion until the end of October, where you can snip out a coupon and present it at a Merlin Entertainment-operated attraction (excluding the London Eye) to gain free entry for a child who is accompanied by a full-paying adult. The voucher can be used until the end of 2016.

However, the Birds Eye vouchers can only be used to buy tickets at the entrance, meaning that you might be better off using other vouchers. To take the example of Alton Towers, an on-the-gate ticket costs £50.40 for an adult and £45.60 for a child, a total of £96.

With the Birds Eye voucher, it’ll be just £50.40.

This example is only relevant to Alton Towers, so it would be wise to take a look around and calculate if you stand to make a decent saving with the other vouchers out there for different parks.

Alternatively, you could take an adult free. Kellogg's is running a promotion with a range of theme parks which offer the chance for one free adult entry for every child or adult ticket purchases.

All you have to do is cut out the voucher from one of the promotional cereal boxes.

[Related story: Wales named cheapest UK holiday destination]

Spend supermarket points

You can spend Nectar points and Tesco Clubcard points to get money off certain parks and attractions. For example, 500 Nectar points are worth £5 in discount vouchers at quite a few attractions.

One of the best theme park offers from Tesco right now is the chance to pay £9.50 in Clubcard vouchers to receive free entry to Blackpool Pleasure Beach, which has a regular gate price of £30.

Sign up to mailing lists

This isn't applicable in all cases but if you sign up to a park’s mailing list they may send you discount codes or vouchers to use.

Earn points on your everyday spending to use on days out with a reward credit card: compare them now