A move to make the default contribution rate to KiwiSaver 4 percent could give a median-income earner an extra $100,000 in their accounts at retirement.

Lifting the default rate from 3 percent of income to 4 percent, matched by a person's employer, was one of a range of suggestions made by the Retirement Commission this week to improve the savings scheme.

Commissioner Jane Wrightson said balances were lower for all age groups than would be expected after 18 years of the scheme, and change was needed.

Increasing the amount you contribute can make a big difference over an investing lifetime.

A 20-year-old joining the scheme earning $65,000 a year and contributing 3 percent plus an employer's 3 percent would have about $300,000 at 65, according to Sorted's calculator.

If the rate was lifted to 4 percent plus 4 percent, they would have $400,000.

Here are four other changes that you can make to improve your outcome:

Check your fund type

Getting your KiwiSaver fund type right for your own circumstances can make a significant difference to your investing outcome.

If you have a while until you need the money, you can often afford to take a bit more risk.

Growth funds tend to be more volatile than balanced or conservative options, but can deliver better returns over the long term.

For that hypothetical 20-year-old, switching from a balanced fund to a growth fund would have given an extra $80,000 at retirement, or a total of about $380,000, even on the 3 percent plus 3 percent contribution rate.

Check you're getting value for money

All KiwiSaver managers charge fees for their services, and what they cost can vary a bit. In general, active managers, which make active choices about which investments they put your money into, tend to charge a bit more than their passive counterparts.

What is usually most helpful is to compare after-fee returns.

That will give you more of a guide as to whether you are getting value for money.

Past returns are no guarantee of the future but if you look over a longer time horizon, you may be able to see patterns of some funds generally delivering better returns.

Understand the impact of a first-home withdrawal

KiwiSaver is a significant part of most people's first home-buying plans.

In the year to April, $129.1 million was withdrawn from KiwiSaver for first-home purchases.

It is hard to argue with this as a financial decision - having a freehold house in retirement can make a big difference to how easy it is to get by.

But it does make a difference to your final outcome.

If that 20-year-old wanted to withdraw her savings in 13 years' time, she might have $78,000 saved for a deposit, if she had been in a growth fund (she would probably need to dial down the risk close to the time of withdrawal).

However, that would lower her balance at 65 to $251,902.

Make voluntary contributions

If you are self-employed or out of the workforce for a while, it can be easy to forget about your KiwiSaver.

Time spent not saving can make a difference, though.

If that 20-year-old paused contributions to her growth fund in 10 years' time, for 12 months, it could reduce her final balance by $10,000.

If she was out for another year, it would lower her final balance to $363,367.

A payment of just over $20 a week is required throughout the year to contribute enough to get the full $521 member tax credit from the government, which is available to people who contribute at least $1,042.

That probably won't grow your balance as quickly as if you were making contributions from a salary, but it keeps you moving in the right direction in the meantime.