Turn £800 or less into £5,400+, cat w arning, 1p Walkers, 22mths 0%, buy new clothe s 2nd hand, Blue Peter badges

Important. Are you under age 73?

Martin: 'You may be able to pay £800, or far less, to gain £5,400 or more, but the clock's ticking! It's all about extra National Insurance (NI) years'

And... finally, many can now do it online

While 'boosting your state pension' doesn't sound sexy, it's the MOST LUCRATIVE THING many can do with their money. To whet your appetite, let's start with one of huge numbers of successes we've had both after I covered it on TV (see my 5-min video explainer) and in our full state pension boosting guide.

It's from Martin Clark who kindly tweeted me last year: "@MartinSLewis You are a star, sir. I asked about my voluntary National Insurance contributions and I was 4 years short. If I pay £2,536 (1 year is £63.40), I get an extra £20.83 a week. Over 20 years I'll get an extra £21,000. Thank you." (I edited out the bit where he said I should be Chancellor - heaven forbid!)

This is all about the 'new' state pension introduced in 2016, which applies to all men born after 5 April 1951 and women after 5 April 1953.

To get the FULL state pension, you need 35ish - and it really is an 'ish', it can vary widely - qualifying National Insurance (NI) years. These usually come from working, looking after children, or via some benefits. Yet many are missing past NI years, commonly due to years abroad, low incomes, career breaks or not claiming credits.

This is a big, occasionally complicated transaction. So I want to take you through it step-by-step. Please don't skip any. That could cost you.

Step 1) Two important checks EVERYONE should make. They're simple and only take a couple of minutes. The links take you through to easy help.

Step 2) Check if you can plug NI gaps for free - it could save you £1,000s. While NI years are usually added to your record automatically, in some cases they need claiming. If you didn't do that, likely as you weren't aware, you can back-claim. We've a full list of free NI years to claim, but here are what I suspect are the three biggest...

Step 3) Missing years from 2006 to 2018? Decide soon if it's 'likely' worth buying years. It oft depends on your age...

Step 4) The most you'll pay for the old years is £824. This can typically net you an 'inflation-proofed' £5,000+. The exact cost of topping up a full voluntary NI year varies slightly depending on which year it is. For employees, class 3 contributions cost...

- 2006/07 to 2019/20: £824.20 for a full year (or £15.85 a week)
- 2020/21: £795.60 for a full year (or £15.30 a week)
- 2021/22: £800.80 for a full year (or £15.40 a week)
- 2022/23: £824.20 for a full year (or £15.85 a week)

If you're self-employed, you can buy class 2 contributions a lot cheaper, for around just £160/yr.

Each extra year typically adds £329 annually to your state pension

This means, even if you had to pay for the whole year, you'd get back what you put in after about two and a half years of state pension. And every year you get your pension after that is profit. We've built a simple State pension NI contribution top-up calculator to help with the maths, though this graph gives you an idea.

A man living for the typical life expectancy would get a total £5,400 back, a woman £6,100 as life expectancy is longer. There are things that can lower the return though, including...

- If you die sooner, thus don't collect your pension for as long.
- If the extra pension income (which is taxable) takes you up a tax threshold, so you pay a higher rate of tax on the amount earned above that threshold (see income tax rates). It's still worth doing though.
- If you were only a couple of hundred quid a year below the state pension, you obviously wouldn't get the full gain from buying a year (you'll find this out in step 5).

Pensions are, mostly, inflation-proofed too

The state pension has long had a 'triple lock', meaning it must go up by the highest of a) 2.5% b) Consumer Prices Index inflation or c) average earnings. This may change, but most likely if it did, it'd still be inflation-proofed.

Step 5) Think buying NI years is right for you? Before you pay out... some important safety checks.

Even if you've passed all the checks, you need actual calculations, or you may pay for years that won't help, or are unnecessary. Until now, that means getting advice via a bespoke (often clogged) phone line. Now some people can finally do this online, which should take some pressure off the phones, though if in any doubt, I'd still do it by phone.

a) Who CAN'T do this online... You won't be able to if:
- You're at state pension age or within 4mths 8 days of it.
- You're filling gaps from self-employment or when you worked abroad.
- You hold a 'Married Women's Reduced Rate Election' certificate.
- You're eligible for 'Home Responsibilities Protection'.

b) If you can and want to do it online... Under the new Check your state pension forecast tool, you'll be shown your state pension forecast, NI record, payable gaps, and if you can pay for gaps online. It'll then either decide you've a complex case and you must do it by phone (see below) or let you select the year(s) to pay for, in full, online via bank transfer or via Open Banking. You can't pay in instalments.

PS: HM Revenue & Customs (HMRC) hasn't been great at giving us info on this, nor would allow us screengrabs to help. So we could do with your feedback on how the new online tool works for you.

c) How to do it via phone and get 1-on-1 help. Which number you call depends on your age...

- Under state pension age? Call the Future Pension Centre.
- At or above state pension age? Call the Pension Service.

While many have told me it can be a pain in the bum to get to speak to someone on these lines, once they do, most say it's brilliantly helpful. Such as Tom: "A huge THANK YOU about the NI advice and phoning the pensions people. I was missing 9yrs. I phoned to be told all I needed to buy was 7yrs to qualify me for an extra £40/wk [so £2,000/yr]. If I hadn't phoned, I'd probably have paid the full £7,500 and lost about £1,800. I'm now looking forward to receiving the full pension."

d) What they won't tell you online or on the phone. The advice doesn't cover every situation. The issues are mostly ones I've already mentioned, but to be sure:

- They won't usually tell you if you're entitled to free years.
- They won't tell you if it will push you into a higher tax bracket.
- They won't tell you that if you're on a very low income, and would have got Pension Credit, this may reduce that.