Moving to part-time hours: compare gross pay and cash flow
Model a shorter working week without assuming every deduction falls proportionally.
Reducing paid hours changes more than the annual salary headline. To estimate the cash effect, calculate the new gross salary first and then recalculate deductions on that amount.
Establish the full-time baseline
Write down the annual salary and the weekly paid hours attached to it. A $75,000 salary for 40 hours gives a different pro-rata calculation from $75,000 for 37.5 hours. Confirm which baseline the employer uses instead of assuming that every full-time role has the same hours.
Calculate the hours fraction
Moving from 40 hours to 24 hours means working 60% of the baseline. The modelled gross salary is therefore $75,000 × 24 ÷ 40 = $45,000. Moving to 32 hours gives 80%, or $60,000.
| Annual gross | Income tax | ACC | Employee KiwiSaver | Student loan | Annual net |
|---|---|---|---|---|---|
| $45,000.00 | $6,783.00 | $787.50 | $0.00 | $0.00 | $37,429.50 |
| $60,000.00 | $10,220.50 | $1,050.00 | $0.00 | $0.00 | $48,729.50 |
| $75,000.00 | $14,720.50 | $1,312.50 | $0.00 | $0.00 | $58,967.00 |
The table excludes optional deductions and credits to isolate the effect of gross pay. Recalculate with your own settings before using the net figures in a budget. Net pay is not simply the full-time net amount multiplied by 60% because the income-tax calculation changes with earnings.
List what may change separately
Travel and childcare costs may fall, stay the same or change in a less obvious way. A shorter day on five days can have different costs from three full days, despite the same weekly hours. Use your own quotes and schedule. Keep allowances, bonuses and non-cash benefits separate until their treatment is confirmed.
Avoid double-counting unpaid time
If the pro-rata annual salary already describes a full paid year at the new hours, do not reduce it again for paid leave. If there will be additional unpaid weeks, model those deliberately as a different scenario. Record the assumptions so you can explain why two calculations differ.
Turn the estimate into a decision
Compare average monthly cash pay, changed work-related costs and an allowance for irregular bills. Save both the current and proposed scenarios. The calculator does not amend your employment agreement or establish benefit entitlements; those need confirmation through the relevant process.
Calculate pro-rata salary · Income-tax rate source ↗
Questions or corrections?
Send the relevant page and a non-sensitive example through our contact form. Read our calculation methodology to see the scope of the model.