Around a million Australians were working a second job before the pandemic hit.

While that number reportedly has fallen by almost 20% since March as jobs dried up, many workers are still relying on multiple jobs in order to make ends meet.

If you have more than one job, here's what you need to know.

For example, if you are earning $50,000 at your first job, your second job is taxed from that level and the higher the income from your first job the higher your marginal tax rate will be.

However, the second job won't take into account what you earn on the first job but after you tick the box not to claim the tax free threshold, the ATO has a tax table based on the income you earn from the second employer who will then deduct that tax.

"Invariably from experience, if you've worked two jobs, there will still be a shortfall on tax that you will have to pay at year end," says Mr Taxman Adrian Raftery.

"If the marginal tax rate is 39c in dollar including the Medicare levy, you have to make sure that at least 39% tax has been deducted on your second job's salary, in general ,if you look at tax rate tables by ATO, it's not quite at that mark."

It's also important to factor in your HELP (previously HECS), which kicks in this year 2020-21 once your income exceeds $46,630 it is payable on your full income, that is, from both jobs combined.

This might mean that if you start earning $68,000 made up of $46,000 from your first job and $22,000 on your second job that all of a sudden you are paying back 4% on your full income which might be a $3000 tax bill you hadn't necessarily prepared for, Raftery says.

"There's nothing worse than when you lodge a tax return and you're hoping to get a refund and you get a bill for a few grand instead; effectively you're chasing your tail then," he says.

"I'd encourage people to have extra and above taken out from second job to have a buffer and receive a refund at the end of the year rather than try and find any pennies to pay tax debt as it arises."

All you have to do is inform your payroll clerk to take more tax out - 39% tax or 45% or 50% and any excess will be returned through a tax refund at the end of the year.

If you've had too much taken out lodge your return ASAP and you have a nice amount of saving but if you do have a tax debt you might want to defer lodgement as late as possible - 31 October if you're lodging it yourself or May the following year if you're using a tax agent.

A benefit you can claim from having two jobs is that you can deduct the cost of travelling between two jobs, on the same day, Raftery says.

You can't claim if you're working one job Monday to Friday and the other is Saturday and Sunday, but if you're working an office job between 9am to 5pm Monday to Friday and then working at a pub afterwards pulling a few schooners you can claim travel between the two worksites.

If you're doing a lot of travel you might like to do a log book and claim a percentage of the running costs of your car.

Another way to decrease your tax bill if you are earning extra money and are being taxed at a higher rate is to salary sacrifice into superannuation - an incentive to save for the future and decrease your tax.

Original article published by Money Magazine here on 16 September 2020.