Tax cuts have taken effect, though you may still have a little wait before you see the impact in your bank account, depending on your pay cycle.

The amount on offer varies depending on your income level. A single pensioner is set to get $4.31 a fortnight. Someone on $70,000 is in line for $30.75. Someone on $110,000 is set to get just over $40 a fortnight.

But what might you do with that extra money?

We've run the numbers based on a $20-per-week tax cut, to have a look at some of the options.

Pay off your mortgage faster

Any extra you can pay off your home loan will have an impact, because it goes straight on to the principal.

If you have a home loan with $500,000 left and 20 years to pay, with a 6.85 percent interest rate, and can now pay an extra $20 a week in repayments, you could save more than $22,000 over the life of your loan.

Add it to your KiwiSaver

A 40-year-old with $40,000 saved in KiwiSaver, earning $70,000 a year and contributing 3 percent plus 3 percent from an employer in a balanced fund might be on track to save $195,010 at retirement, according to Sorted's calculator.

Topping that up by $20 a week would lift their savings to $219,949 at 65.

Buy groceries

According to Stats NZ, $20 would have got you a 1kg block of mild cheddar (average $10.03) and a dozen eggs ($9.41) in June.

Buy power

Your heat pump probably costs about 45c to 50c an hour to run, so you could turn it on for an extra 40 hours.

Invest it in a managed fund

If you could invest $20 a week in a fund giving you 5 percent return a year, you would have more than $70,000 after 30 years - not accounting for fees or taxes.

Charity

You could give $20 a week to charity and then claim 33.3 percent of it back in your tax return. Tearfund charges $20 for a donation of a chicken.

Fuel up your car

You could get about seven-and-a-half litres of petrol for $20, maybe about enough to drive 100km, depending on how economical your car is.

Pay off your credit card

If you have a credit card with a $5000 balance and an interest rate of 20 percent, and you're paying it off at a rate of $500 a month, adding an extra $20 a week will shave about two months off the time it takes you to clear the balance.