The better question is probably when will the last fraction of a coin be mined. The block reward started at 48 coins per block in August 2011 and halves every 218,750 blocks. The table below shows the block reward out to the maximum eight decimal places. It appears the last decimal turns to zero around 2029. So 2028 will probably see the last block reward, although it gets pretty negligible years before. Then again, what is "negligible" will depend on the value of i0coin at the time.
Block No. of
Date Block# Reward Coins % Mined
--------- ------- ------- ------ --------
8/16/2011 1 48 48 0.00%
2/20/2012 218751 24 10,500,024 50.00%
8/26/2012 437501 12 15,750,012 75.00%
3/2/2013 656251 6 18,375,006 87.50%
9/6/2013 875001 3 19,687,503 93.75%
3/14/2014 1093751 1.5 20,343,752 96.88%
9/18/2014 1312501 0.75 20,671,876 98.44%
3/25/2015 1531251 0.375 20,835,938 99.22%
9/29/2015 1750001 0.1875 20,917,969 99.61%
4/5/2016 1968751 0.09375 20,958,984 99.80%
10/10/2016 2187501 0.046875 20,979,492 99.90%
4/16/2017 2406251 0.023438 20,989,746 99.95%
10/21/2017 2625001 0.011719 20,994,873 99.98%
4/28/2018 2843751 0.00585938 20,997,436.53 99.99%
11/2/2018 3062501 0.00292969 20,998,718.26 99.99%
5/9/2019 3281251 0.00146484 20,999,359.13 100.00%
11/13/2019 3500001 0.00073242 20,999,679.57 100.00%
5/20/2020 3718751 0.00036621 20,999,839.78 100.00%
11/24/2020 3937501 0.00018311 20,999,919.89 100.00%
5/31/2021 4156251 0.00009155 20,999,959.95 100.00%
12/5/2021 4375001 0.00004578 20,999,979.97 100.00%
6/12/2022 4593751 0.00002289 20,999,989.99 100.00%
12/17/2022 4812501 0.00001144 20,999,994.99 100.00%
6/23/2023 5031251 0.00000572 20,999,997.50 100.00%
12/28/2023 5250001 0.00000286 20,999,998.75 100.00%
7/4/2024 5468751 0.00000143 20,999,999.37 100.00%
1/8/2025 5687501 0.00000072 20,999,999.69 100.00%
7/15/2025 5906251 0.00000036 20,999,999.84 100.00%
1/19/2026 6125001 0.00000018 20,999,999.92 100.00%
7/27/2026 6343751 0.00000009 20,999,999.96 100.00%
1/31/2027 6562501 0.00000004 20,999,999.98 100.00%
8/7/2027 6781251 0.00000002 20,999,999.99 100.00%
2/11/2028 7000001 0.00000001 21,000,000.00 100.00%
8/18/2028 7218751 0.00000001 21,000,000.00 100.00%
2/22/2029 7437501 0.00000000 21,000,000.00 100.00%
8/29/2029 7656251 0.00000000 21,000,000.00 100.00%