COVID-19 NZ, USA, China: When is the midpoint? When will an outbreak be over?

Our final fate

What day may be the end date
For this bad COVID outbreak
In case numbers augment
They say add ten percent
What may be the sad death-rate

Alan Grace
13 May 2020

In this post we investigate how long it will be until an outbreak is over and the total number of cases.


You may like to look at these posts:

In the above post we estimated the midpoint for China for COVID-19.

24 15 February 2020 1,669 143 3,195
23 14 February 2020 1,526 143 2,909

“Where a single day is used for the total this day is the midpoint, and the number of days to reach the total is twice the number of days.

Where two days have been used, the midpoint is halfway between these two days, and the number of days to reach the total is twice this.

We are currently accepting 3195 (3200) as the likely death total in China.

If we had chosen one day earlier, adding 10% would have become more important. If we add !0% on to 2909 (see table above) we get 3,199 (c.f. 3195)!

For 3195 total deaths, the midpoint is 23.5 and the number of days to reach 3195 is therefore 47.”

Day 47 for China is 9 March when we had a total of 3136 deaths.

Five days later on 14 March, the total rose to 3,199 deaths.

However two months later on 14 May, there were still 17 new cases yesterday.

The number of deaths is 4,633 but once you subtract the adjustment of an extra 1290 deaths on April 17 (because the China was only counting hospital deaths before this date), the number of deaths would have been 3,343 deaths.

We note that 14 May is over two months after our 14 March date when we had a total of 3,199 deaths.

We need to therefore allow for an extra two months for the USA outbreak in case there is a long tail in the USA like China has had.

For the USA, look at this table from our previous post:

Deaths Add 10%
Date Cumulative 21+22 22+22 22+23
21-Apr 45,536 102,773
22-Apr 47,894 105,366.8
23-Apr 50,234 107,940.8

22 April was day 93 (this was around our estimated midpoint).

Day 186 (2 x 93) is 24 July. We allow an extra week (until 31 July) for the USA to reach the total of 105,000  deaths.

We are likely to need to add the extra two months to allow for a long tail.

This brings us to 31 September.

In the previous post, we extended this to 20 October.


As previously, the range for the number of deaths is from 105,500 to 130,500.

We adopt 125,500 deaths.

The range for the number of cases is from 1.75 to 2.2 million cases, with the expected number of cases likely to be around 2.1 million cases.

This are our final totals.

We consider the USA outbreak is likely to have finished near this date if there is no secondary/new outbreak in the USA.


For New Zealand we used case estimates:



New Zealand currently has had 1497 cases of COVID-19 and 21 deaths.

The cumulative number of cases for these days (33 and 34) are 647 and 708 giving a total for these two days of 1355 cases.

We add on 10% to allow for a long tail, giving 1490 cases (rounded to 1500 in previous posts).

For New Zealand 1500 cases is the bottom end of our range.

We estimated the midpoint at Day 33.5, making Day 67 the estimated date for 1355 cases.

Day 67 is 4 May when we had a cumulative total 1487 cases.

Just over one week later we have 1497 cases.

We need to wait to see how long the tail will be (if it is long) in New Zealand.

New Zealand moves down to Lockdown Level 2 tonight at 11.59pm.

We hope this does not lead to an increase in the number of cases.


My other COVID-19 posts can be found here:

Data for my posts can be found at:

I share my posts at:

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